Battery system for a vehicle with severable connections

ABSTRACT

A battery system for storing electrical power and supplying electrical power to a vehicle is disclosed. The system includes multiple battery packs, each with a plurality of cells. The cells in each battery pack are electrically connected with one another and the multiple battery packs are also electrically connected with one another to combine the total energy output of the cells of the system. The electrical connections between at least some of the cells include a severable feature, whereby the electrical connection is severed locally at the severable feature in response to an impact force that is in excess of a predetermined magnitude and/or an overcurrent/overtemperature condition.

PRIORITY CLAIM

The present application claims priority to the following Chinese PatentApplications, which are hereby incorporated by reference:

-   1) Chinese Patent Application No. 200820183400.0 (docket no.    081632), filed Dec. 12, 2008.-   2) Chinese Patent Application No. 200820176590.3 (docket no.    081634), filed Dec. 5, 2008.-   3) Chinese Patent Application No. 200810179278.4 (docket no.    081633), filed Dec. 4, 2008.-   4) Chinese Patent Application No. 200820179656.4 (docket no.    081631), filed Dec. 4, 2008.-   5) Chinese Patent Application No. 200820180541.7 (docket no.    081630), filed Dec. 3, 2008.-   6) Chinese Patent Application No. 200810217018.1 (docket no.    081483), filed Oct. 10, 2008;-   7) Chinese Patent Application No. 200820116496.9 (docket no.    080394), filed Jun. 30, 2008;-   8) Chinese Patent Application No. 200810145734.3 (docket no.    080932), filed Aug. 14, 2008;-   9) Chinese Patent Application No. 200810135478.X (docket no.    080933), filed Aug. 7, 2008;-   10) Chinese Patent Application No. 200810135477.5 (docket no.    080934), filed Aug. 7, 2008;-   11) Chinese Patent Application No. 200810142082.8 (docket no.    081178), filed Aug. 27, 2008;-   12) Chinese Patent Application No. 200810142090.2 (docket no.    081180), filed Aug. 27, 2008;-   13) Chinese Patent Application No. 200820146848.5 (docket no.    081181), filed Aug. 27, 2008;-   14) Chinese Patent Application No. 200820146851.7 (docket no.    081183), filed Aug. 27, 2008;-   15) Chinese Patent Application No. 200820146849.X (docket no.    081184), filed Aug. 27, 2008;-   16) Chinese Patent Application No. 200810142084.7 (docket no.    081185), filed Aug. 27, 2008;-   17) Chinese Patent Application No. 200810142085.1 (docket no.    081186), filed Aug. 27, 2008;-   18) Chinese Patent Application No. 200810142089.X (docket no.    081187), filed Aug. 27, 2008;-   19) Chinese Patent Application No. 200810142086.6 (docket no.    081188), filed Aug. 27, 2008;-   20) Chinese Patent Application No. 200810142087.0 (docket no.    081189), filed Aug. 27, 2008;-   21) Chinese Patent Application No. 200810142088.5 (docket no.    081190), filed Aug. 27, 2008;-   22) Chinese Patent Application No. 200810142080.9 (docket no.    081192), filed Aug. 27, 2008;-   23) Chinese Patent Application No. 200810142083.2 (docket no.    081191), filed Aug. 27, 2008. and-   24) Chinese Patent Application No. 200720196395.2 (docket no.    071593), filed Dec. 25, 2007.

BACKGROUND

1. Technical Field

The present application is directed to battery cells and systems and,more particularly, to lithium ion battery cells and systems that may beused in a vehicle, such as an electric and/or hybrid vehicle, having anelectric drive motor.

2. Related Art

Re-chargeable batteries, such as lithium ion polymer batteries, have awide range of applications. These include, for example, laptopbatteries, cell phone batteries, as well as power for other personalelectronic devices. Such devices require low weight batteries having amoderate power output. However, lithium ion polymer batteries are alsocapable of providing power to devices needing substantially more poweroutput than the personal electronic devices noted above. For example,high output lithium ion polymer batteries may be used to powerindustrial equipment, high power communications facilities, mobilevehicles, etc. The use of high output lithium ion polymer batterysystems may be particularly significant in the area of mobile vehiclepropulsion.

The public has become increasingly sensitive to cost and environmentalissues associated with the use of fossil-based fuels. One concern is theemissions from vehicles burning fossil-based fuels and the correspondingpollution.

Alternatives to such vehicles include electric vehicles that are solelydriven by electric motors, and hybrid electric vehicles that employ bothelectric motors and fossil-based fuel engines. These alternatives arelikely to play an increasingly important role as substitutes for currentvehicles.

Although consumers are attracted to the environmental benefits of pureelectric and hybrid vehicles, they want vehicles which use electricmotors to have the same general characteristics as their fossil-fuelcounterparts. Battery performance and safety issues must be overcome toachieve these goals. To this end, lithium ion batteries are preferableto other more conventional battery types. Lithium ion batteries areuseful for this purpose in that they have a high energy density whichreduces the amount of space needed for the battery in the vehicle.Further, they may be constructed so that they weigh less than the moreconventional battery types.

Battery systems for use with electric motors employed in pure electricand hybrid vehicles are currently deficient in many respects. Individualbattery cells of the battery system are frequently heavy, bulky, andunreliable. Further, current battery cells are neither constructed norused to effectively provide the high power output needed to acceleratethe vehicle at an acceptable acceleration level. Still further,individual battery cells use electrochemistry, cell core constructions,electrical interconnections, and shell constructions that are oftenunreliable, unsafe, and generally not suitable for use in electricalpowered vehicles.

To overcome the power deficiencies associated with individual batterycells, attempts have been made to interconnect multiple individualbattery cells with one another so that their combined power outputprovides the necessary driving power. The interconnections between theindividual battery cells, again, are often unreliable. Further, littlehas been accomplished to ensure the safety of such multi-cell batterysystems. Short-circuits as well as explosions have not been adequatelyaddressed. High power output battery systems must be constructed toaddress issues such as performance, longevity, reliability, and safetyif they are to find a place in the large number of applicationsavailable to such systems.

SUMMARY

A battery system for storing electrical power and supplying electricalpower to a vehicle is disclosed. The system includes multiple batterypacks, each with a plurality of cells. The cells in each battery packare electrically connected with one another and the multiple batterypacks are also electrically connected with one another to combine thetotal energy output of the cells of the system. The electricalconnections between at least some of the cells include a severablefeature, whereby the electrical connection is severed locally at theseverable feature in response to an impact force that is in excess of apredetermined magnitude and/or an overcurrent/overtemperature condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereferenced numerals designate corresponding parts throughout thedifferent views.

FIG. 1 is a cross-sectional view through an exemplary multilayer batterysheet that may be used to form a coiled battery core.

FIG. 2A is a perspective view of a flattened coiled core used in abattery cell.

FIGS. 2B-2D show an alternative embodiment of a core where the sheetsforming the core are not coiled.

FIG. 3 is an exploded view of the anode end of a battery cell 300 havingthe coiled core of FIG. 2A.

FIG. 4 is a schematic view through a cross-section of battery cell 300.

FIGS. 5 and 6 illustrate one manner of forming the regions of the anodesheet and/or cathode sheet which are proximate the exposed substrates.

FIG. 7 is a cross-sectional view of one example of a coiled core.

FIG. 8 shows one embodiment of a frangible bent connector.

FIG. 9 illustrates a further embodiment of a frangible bent connector.

FIG. 10 shows how the bent connector of FIG. 8 may be used tointerconnect adjacent battery cells.

FIG. 11 shows another structure for interconnecting adjacent batterycells.

FIGS. 12 and 13 show a connection structure that may be utilized tobring the core of a battery cell to an optimal operating temperature.

FIG. 14A shows one manner of connecting a multiple core battery cell tothe bent connector of FIG. 8.

FIG. 14B shows one manner of connecting a single core structure of abattery cell to the bent connector of FIG. 8.

FIG. 15 is a plan view of a gasket used at each end of the protectiveshell of the battery cell.

FIGS. 16 and 17 show one manner of sealing the end of the protectiveshell that surrounds the periphery of the coiled core.

FIGS. 18-20 show one embodiment of a blow out assembly that may be usedon the end cover assembly of a battery cell.

FIGS. 21 and 22 show alternative pressure relief structures that may beused to supplement and/or replace the blow out assembly shown in FIG.18.

FIG. 23 is a block diagram of a battery pack in which multiple batterycells are interconnected with one another and grouped within a singlehousing.

FIGS. 24 through 26 illustrate one embodiment of a housing that may beused to form a battery pack.

FIG. 27 shows a connector that may be used to mechanically andelectrically interconnect adjacent battery packs.

FIG. 28 shows how the connector of FIG. 27 may be used.

FIG. 29 shows a battery system that supplies electrical power to andreceives electrical power from a motor/generator of a vehicle capable ofbeing driven by electric power.

FIGS. 30 through 34 illustrate advantages associated with providingconnections to the anode and cathode of a coiled core at opposite endsof the core.

FIGS. 35-41 illustrate further battery cell interconnection structures.

FIG. 41A illustrates a frangible connection structure having a thermallyactivated severing clamp.

FIGS. 42 through 46 illustrate battery cell interconnection structureswhere the terminals of the battery cells are interconnected with oneanother by a bridge connector.

FIGS. 47 and 48 illustrate battery cell interconnection structureshaving gravity assisted overcurrent protection substructures.

FIGS. 49 through 51 illustrate battery cell interconnection structureshaving a thermal expansion structure that separates the battery cellterminals as a result of overcurrent conditions.

FIGS. 52 and 53 illustrate battery cell interconnection structureshaving overcurrent protection substructures based on chemicalinteraction between a chemical released by the substructure and one ormore portions of the terminals/terminals of the battery cellinterconnection.

FIGS. 54-60 illustrate battery cell interconnection structures havingovercurrent protection substructures based on electricalconnections/disconnections provided by the presence/absence of a liquidconductor.

FIGS. 61 through 64 illustrate various embodiments of a protection coverfor the end cover assembly of the battery cell.

FIGS. 65 through 67 illustrate a further embodiment of a blow out vent.

FIG. 68 shows a further embodiment of a connector that may be used tomechanically and electrically interconnect adjacent battery packs.

FIG. 69 shows how the connectors of FIGS. 27 and 68 may be used when thebattery packs are configured in a side-to-side arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Lithium-ion polymer batteries are a type of rechargeable battery inwhich a lithium ion moves between an anode and cathode. The lithium ionmoves from the anode to the cathode during discharge and from thecathode to the anode when charging.

FIG. 1 is a cross-sectional view through an exemplary multilayer batterysheet 100 that may be wound to form a coiled battery core. The batterysheet 100 of FIG. 1 includes three functional components: an anode sheet105, a cathode sheet 110, and a separator sheet 115. The anode sheet 105may include active anode layers 106 disposed on opposite sides of ananode substrate 107. The anode substrate 107 may be formed from one ormore layers of a metal foil, such as copper. The active anode layers 106may be formed from graphite or other carbon-based material. In oneexample, active layers 106 of the anode sheet 105 may be produced using100 grams of natural graphite with 3 grams of polyvinylidene fluoride(PVDF) binder material and 3 grams of acetylene black conductive agentto 100 grams of NI-methylpyrrolidone (NMP). The components may be mixedin a vacuum mixer into a uniform slurry. The slurry may be applied as acoating of about 12 microns thick to each side of substrate 107, such asa copper foil, to form a structure having a combined layer thickness ofabout 100-110 μm. The coated foil may then be dried at a temperature ofabout 90° C. to form the anode 115.

The cathode sheet 110 may include active cathode layers 112 disposed onopposite sides of a cathode substrate 114. The cathode substrate 114 maybe formed from one or more layers of a metal foil, such as aluminum. Theactive cathode layers 112 may be formed from materials such as a layeredoxide (e.g., lithium cobalt oxide), a material based on a polyanion(e.g., lithium iron phosphate), or a spinel (e.g., lithium manganeseoxide), although materials such as TiS₂ (titanium disulfide) may also beused.

In one example, the active layers 112 of the cathode sheet 110 may beformed by combining at least one lithium metal compound with at leastone mixed metal crystal, wherein the mixed metal crystal includes amixture of metal elements and metal oxides. The lithium compound may bea metal intercalation compound that has the general formulaLiM_(a)NbX0_(c), wherein M is a first-row transition metal such as Fe,Mn, Ni, V, Co and Ti; N is a metal selected from the group Fe, Mn, Ni,V, Co, Ti, Mg, Ca, Cu, Nb, Zr and rare-earth metals; X is selected fromelements P, Si, S, V and Ge; and a, b and c have values that render themetal intercalation compound charge-neutral. The metal compound may havethe general formula M_(c)Nd, wherein M is a metal selected from IA, 11A,IIIA, IVA, VA, IIIB, IVB and VB groups in the periodic table; N isselected from 0, N, H, S, SO4, PO4, OH, Cl, F, and C; and 0<c5.4 and0<d56. In other instances, the metal compound may include one or moremembers selected from the group consisting of MgO, SrO, Al₂0₃, SnO₂,Sb₂0₃, Y₂0₃, TiO₂ and V200. The metal compound and the lithium compoundmay be heated or sintered at about 600-900° C. in an inert gas orreducing gas atmosphere for about 2 hours to form the material for thecathode sheet 110.

In a further example, the metal compound may be formed as a mixedcrystal compound with the general formula LiaA1_(—y)B_(y)(X04)b/McNd,wherein: A is a first-row transition metal including Fe, Mn, Ni, V, Coand Ti; B is a metal selected from the group Fe, Mn, Ni, V, Co, Ti, Mg,Ca, Cu, Nb, Zr and rare-earth metals; X is selected from elements P, Si,S, V and Ge; M is metal selected from groups IA, IIA, IIIA, IVA, VA,IIIB, IVB and VB of the periodic table; N is selected from 0, N, H, S,SO4, PO4, OH, Cl, F and C; and wherein 0<a51, 05y50.5, 0<b51, 0<c5.4 and0<d56. Particle sizes may be less than about 10 um, with 3-5 um beingpreferable.

The active cathode material may include a first crystalline compound anda second crystalline compound. The first crystalline compound may bedistributed within the second crystalline compound to form a compositecompound. The first crystalline compound may be prepared by heating acombination of at least one lithium source, at least one iron source,and at least one phosphate source while the second crystalline compoundmay be prepared by heating at least two metal compounds. The secondcrystalline compound may also include one or more members selected fromgroups IA, IIA, IIIA, IVA, VA, IIIB, IVB and VB of the periodic table.

During formation of the active cathode material, a large number ofcrystal defects may be introduced within the intermediary or compositecrystals such that the electronic states and formation of the metaloxides are altered or changed. The metal compound with its mixedcrystalline structure, therefore, may include a large number of oxygenvacancies and missing oxygen atoms. The oxygen vacancies may facilitatecarrier conduction thereby enhancing the conductivity of the mixedcrystal. To this end, the metal compound may have a smaller crystallattice than the lithium compound so that it is received or distributedwithin the lithium compound. Alternatively, the metal compound may bereceived or distributed between two or more large crystal lattices.Still further, the metal compound may reside within grain boundaries ofthe lithium compound. Lastly, the metal compound may be dispersed aboutthe exterior grain surfaces of the lithium compound. In each instance,lithium ion migration serves as a bridge either within a crystal latticeor in between two or more crystal lattices. The lithium ions may befully released for enhanced electrical properties including electricalconductance, capacitance and recyclability.

Preferably, the metal compound may be distributed within a lithium ironphosphate compound to form a composite compound for use in the cathodesheet 110. The metal compound may be distributed within the lithium ironphosphate compound to form a mixed crystal. In one instance, the lithiumiron phosphate compound and the metal compound may have molar ratios ofabout 1 to 0.001-0.1. The cathode material may be doped with carbonadditives scattered between grain boundaries or coated on the grainsurfaces. The doped carbon additive may provide the final cathodematerial product with 1-15% of carbon by weight. The carbon additive mayinclude one or more members selected from the group consisting of carbonblack, acetylene black, graphite and carbohydrate compound.

The composite compound may include a lithium source, iron source,phosphate source and second crystalline compound having aLi:Fe:P:crystalline compound molar ratios of about 1:1:1:0.001-0.1. Inother instances, various Li:Fe:P:crystalline compound molar ratios maybe adopted. The lithium source may include one or more members selectedfrom the group consisting of lithium carbonate, lithium hydroxide,lithium oxalate, lithium acetate, lithium fluoride, lithium chloride,lithium bromide, lithium iodide and lithium dihydrogen phosphate. Theiron source may include one or more members selected from the groupconsisting of ferrous oxalate, ferrous acetate, ferrous chloride,ferrous sulfate, iron phosphate, ferrous oxide, ferric oxide, iron oxideand ferric phosphate. The phosphate source may include one or moremembers selected from the group consisting of ammonium, ammoniumphosphate, ammonium dihydrogen phosphate, iron phosphate, ferricphosphate and lithium hydrogen phosphate.

A method of preparing a mixed crystal lithium iron phosphate cathodematerial includes evenly mixing at least one LiFePO4 compound with amixture compound and heating the resulting mixture to 600-900° C. in aninert gas or reducing gas atmosphere for between about 2-48 hours. Themixture compound may include two or more metal oxides wherein the metalcan be selected from groups IA, IIA, IIIA, IVA, VA, IIIB, IVB and VB ofthe periodic table. The mixture compound provides a mixed crystallinestructure, wherein a method of preparing the mixture compound with thecorresponding mixed crystalline structure includes mixing metal oxidesfrom groups IA, IIA, IIIA, IVA, VA, IIIB, IVB and VB, and heating themixture to 600-1200° C. for between 2-48 hours.

One method of preparing a mixed crystal cathode material includes evenlymixing lithium, iron and phosphate sources and heating them to 600-900°C. in an inert gas or reducing gas atmosphere for at least about 2hours. The resulting mixture can then be combined with the mixed metalcompound having a combination of two or more metal oxides selected fromgroups IA, IIA, IIIA, IVA, VA, IIIB, IVB and VB of the periodic table.In one embodiment, the lithium source, iron source, phosphate source andmixed metal compound are capable of providing Li:Fe:P:mixed metalcompound molar ratios of 1:1:1:0.0010.1. In other embodiments, differentLi:Fe:P:mixed metal compound molar ratios may be adopted. Furthermore,at least one carbon source can be added to the resulting mixture, thecarbon source including one or more of the following without limitation:carbon black, acetylene black, graphite and carbohydrate compound. Theamount of carbon source added to the resulting mixture should be able toprovide the final product with 1-15% of carbon by weight.

The lithium sources used to form the cathode material may include one ormore of the following compounds without limitation: lithium carbonate,lithium hydroxide, lithium oxalate, lithium acetate, lithium fluoride,lithium chloride, lithium bromide, lithium iodide and lithium dihydrogenphosphate. Iron sources include one or more of the following compoundswithout limitation: ferrous oxalate, ferrous acetate, ferrous chloride,ferrous sulfate, iron phosphate, ferrous oxide, ferric oxide, iron oxideand ferric phosphate. When using a trivalent iron compound as a sourceof iron, the ball milling process may include the addition of a carbonsource to reduce the trivalent iron to a divalent iron. Phosphoroussources may include one or more of the following compounds withoutlimitation: ammonium, ammonium phosphate, ammonium dihydrogen phosphate,iron phosphate, ferric phosphate and lithium hydrogen phosphate.

During the grinding in a ball mill, one or more solvents may beintroduced including ethanol, DI water and acetone. In other,embodiments, other mixing media and solvents may be utilized. Inaddition, the mixture can be dried between 40-80° C. or stirred untildry.

The types of inert gases that may be utilized include helium, neon,argon, krypton, xenon, radon and nitrogen. Additionally, reducing gasesincluding hydrogen and carbon monoxide can also be incorporated. Othersuitable gases may also be adopted.

The cathode sheet 110 may be formed using a cathode slurry that includesone of the foregoing active cathode materials. The cathode slurry may beformed by mixing a thickener, the active cathode material, and asolvent. First, the thickener and the solvent are mixed to provide acolloidal solution. The resulting colloidal solution, residual solvent,and the active material are mixed in a double planetary mixer. A portionof the solvent as well as a binder are then provided to the planetarymixer for further mixing.

The colloidal solution, the active cathode material, and solvent may bemixed in the double planetary mixer in accordance with a specifiedmixing sequence. To this end, the colloidal solution, the activematerial, and the solvent may be mixed for about 3-5 minutes at arotation frequency of about 2-20 Hz that decreases to a lower rotationfrequency of about 0-2 Hz. Next, the colloidal solution, the activematerial, and the solvent may be mixed for about 30-50 minutes at arotation frequency between about 35-60 Hz that decreases to a lowerrotation frequency between about 35-60 Hz. At this point, the doubleplanetary mixer may generate a vacuum lasting about 3-5 minutes so thatthe mixing takes place at a pressure of about 0.0005 MPa to about 0.05MPa. The residual solvent and the adhesives are then added to the doubleplanetary mixer and mixed for about 5-10 minutes at a rotation frequencyof about 35-60 Hz that decreases to a lower rotation frequency betweenabout 35-60 Hz. Again, the double planetary mixer may generate a vacuumlasting about 3-5 minutes so that the mixing takes place at a pressureof about 0.0005 MPa to about 0.05 MPa. The mixing then takes placebetween about 20-35 minutes at a rotation frequency that decreases fromabout 10-25 Hz to about 0 Hz.

The proportion by weight of the active material of cathode, thethickener, the adhesives and the solvent may be about100:(0.05-10):(0.01-10):(50-150). The proportion by weight of thesolvent mixed with the thickener may be about 60-90%. When mixed withthe colloidal solution and active material, the proportion by weight ofthe solvent may be about 0.1-30%, and may be about 8-20% when withbinder is added.

The cathode sheet 110 may be formed by coating a conductive substrate,such as an aluminum foil, with the slurry. The slurry may be appliedonto the conductive substrate using a rolling operation, although otherapplication methods may be employed. The conductive substrate and slurryare then dried to form the cathode sheet 110. The cathode sheet 110preferably has a thickness between 100 and 110 μm, although otherthicknesses may also be used.

The separator sheet 115 may be a micro-porous polypropylene and/orpolyethylene electrolytic membrane. Such membranes are available from USCelgard of Charlotte, N.C.

With reference again to FIG. 1, the anode sheet 105 includes a region inwhich the substrate 107 of the anode sheet 105 does not include activeanode layers 106. Rather, the copper substrate 107 is exposed tofacilitate electrical connection with the anode sheet 105. The exposedregion of substrate 107 extends substantially along the entire length ofthe anode sheet 105 so that the first edge of the anode sheet 105defines a conductive region 107 when the battery sheet 100 is wound toform a coiled core 200 (see FIG. 2). The exposed region of substrate 107may be formed by limiting the area to which the active anode layers 106are applied to the substrate 107. Additionally, or alternatively, theexposed region of substrate 107 may be formed after the application ofthe active anode layers 106 by selectively removing the active anodelayers 106 from the substrate 107 along a predetermined width of theanode sheet 105. This removal may be accomplished using a mechanicalremoval technique and/or chemical removal technique.

The cathode sheet 110 includes a region in which the substrate 114 ofthe cathode sheet 110 does not include active cathode layers 112.Rather, the aluminum substrate 112 is exposed to facilitate electricalconnection with the cathode sheet 110. The exposed region of substrate112 extends substantially along the entire length of the cathode sheet110 so that an edge of the cathode sheet 110 defines a conductive region114 when the battery sheet 100 is wound to form the coiled core 200 ofFIG. 2A. The exposed region of substrate 114 may be formed by limitingthe area to which the active cathode layers 112 are applied to thesubstrate 114. Additionally, or alternatively, the exposed region ofsubstrate 114 may be formed after the application of the active cathodelayers 112 by selectively removing the active cathode layers 112 fromthe substrate 114 along a predetermined width of the cathode sheet 110.This removal may be accomplished using a mechanical removal techniqueand/or chemical removal technique.

As shown in FIG. 2A, the anode sheet 105, cathode sheet 110, andseparator sheet 115 may be wrapped to form the coiled core 200. Theexposed substrate 114 forms a multilayer current collector structure forthe cathode of the coiled core 200 while the exposed substrate 107 formsa multilayer current collector structure for the anode of the coiledcore 200. The current collector for the cathode and current collectorfor the anode are disposed at opposite ends of the length of the core200 and provide low resistance contacts that may carry a substantialamount of current. Forming the current collectors at opposite sides ofthe coiled core 200 also simplifies the manufacturing process.

The current collectors may be formed in a number of different manners.For example, the current collectors may be formed solely from theexposed substrate layers. Additionally, or in the alternative, thecurrent collectors may be formed by attaching a conductive ribbon ofmaterial along a length of each of the anode and cathode sheets,respectively, prior to or after winding.

The exterior layer of the coiled core 200 may be an insulator. In oneexample, the separator sheet 115 is longer than the anode sheet 105 andcathode sheet 110. As such, the anode sheet 105 and cathode sheet 110are terminated in the wrapping operation before the end of the separatorsheet 115 is reached. The excess length of the separator 105 is thenwrapped about the core 200 a predetermined number of times (e.g., two ormore) to form the exterior insulating layer 115. This constructionsimplifies the manufacturing of the core 200 and, further, increases thehomogeneity of the core structure.

Once the coiled core 200 has been formed, the exposed layers of theanode substrate 107 and cathode substrate 114 are compressed to changetheir shape so that the outside cross-sectional area of each end portionof the coiled core 200 is less than the interior cross-sectional area ofthe core 200. To this end, the exposed layers of the anode substrate 107of the coiled core 200 may be welded to one another, secured to oneanother with a mechanical fastener, and/or secured to one another usingan adhesive, etc. Preferably, the exposed layers of the anode substrate107 are secured with one another by compressing them together, weldingthem together along the entire length or portions of the length of theexposed substrate 107 to form a single anode current collectorstructure. The layers of the cathode substrate 114 may be formed in asimilar manner as the layers of the anode substrate 107.

An alternative structure for the core 200 is shown in FIGS. 2B through2D. In this embodiment, multiple anode sheets, cathode sheets, andseparator sheets are layered adjacent one another. However, unlike thepreviously described core structure, the sheets forming the core are notwound to form a coil. Rather, the core 200 is comprised of a pluralityof planar sheets, such as shown in the arrangement of FIG. 2B.Preferably, the end sheets of the core 200 are insulator sheets and,more preferably, one or more separator sheets 115. A top plan view ofthis embodiment of the core 200 is shown in FIG. 2C while a side planview is shown in FIG. 2D. As illustrated, the insulator/separator sheetspreferably extend beyond the lateral edges of the stacked cathode andanode sheets and may be wrapped around the side edges to isolate thecathode and anode sheets from one another. Alternative methods forsealing the stacked cathode and anode sheets to prevent undesiredcontact between them and to prevent environmental exposure may also beused. Although the current collectors 114 and 107 of FIGS. 2B through 2Dare formed from the substrate layers of the anode and cathode sheetmaterial, they may also be formed as ribbons that are connected to theindividual stacked substrate layers.

FIG. 3 shows an exploded view of the anode end of a battery cell 300having the coiled core 200 (not shown but implied in FIG. 3). In FIG. 3,battery cell 300 includes a protective shell 305 that receives thecoiled core 200. Current collector 310 electrically engages a first end320 of a connection structure 325 through an end cover assembly 335. Asecond end 330 of the connection structure 325 extends through acorresponding cover plate/end cap 335 to provide an exterior contact forthe anode of the battery cell 300.

As shown in FIG. 3, the protective shell 305 is rectangular in shape andis dimensioned so that the core 200 fits snugly within its interior.Although the shell 305 (and, as such, core 200) may have variousdimensions, protective shell 305 may have a width W and a height H,where W is greater than about 50 mm and H is greater than about 100 mm.Preferably, the ratio between the width and height of the shell 305corresponds to the following equation:

0.18<W/H<0.5

This relationship is also suitable to generally define the dimensions ofthe core 200, and is particularly well-suited when the battery cell 300is a high capacity, high power output battery.

When the W/H ratio is larger than 0.5, the width of the battery cell 300is very large, and the total surface area of the shell 305 may not becapable of withstanding the pressure generated within its interiorthereby causing it to fail and/or distort. This may create asafety/security risk. When the W/H ratio is smaller than 0.18, theheight of the battery cell 300 is very small, so that the battery cell300 is very thin. The available volume available to the core 200 withinthe protective shell 305 is quite small and does not favor theaccommodation of a high capacity, high current core.

FIG. 4 is a schematic view through a cross-section of battery cell 300.In this example, the connection structure 325 includes an angledconnector 405 that extends through cover plate/end cap 335. Here, theangled connector 405 is substantially Z-shaped. Current collector 310may be formed in the manner described above. For simplicity, the currentcollector 310 of FIG. 4 only illustrates a single anode currentcollector strip. A flexible connection piece 410 electrically connectsthe angled connector 405 to the current collector 310. The flexibleconnection piece 410 may include multiple metal foil layers, such ascopper, that have been annealed and welded to both the angled connector405 and the current collector 310. A similar technique may be used toconnect the cathode collector to a corresponding angled connector of aconnection structure. However, the flexible connection piece between theangled connector and the cathode current collector may be formed frommultiple aluminum foil layers that have been annealed and welded to boththe angled connector and cathode current collector. The use of this typeof interconnection structure facilitates the ease with which a batteryusing coiled core 200 may be manufactured. Further, the interconnectionstructure may be used to provide a low resistance, high current paththrough the battery. Still further, this structure may be used todissipate heat thereby promoting battery safety.

FIGS. 5 and 6 show one manner of forming the regions of the anode sheet105 and/or cathode sheet 110 which are proximate the exposed substrates107 and/or 114, respectively. Only the region proximate the exposedsubstrate 107 is described, although the corresponding region proximatethe exposed substrate 114 may have the same basic structure.

In FIGS. 5 and 6, the anode sheet 105 has a total width 505. The activelayers 106 of the anode sheet 105 are applied along a width 510 of thesheet leaving an uncoated region having a width 515. Alternatively, theuncoated region may be formed by removing a portion of the activecomponent of the anode sheet 105. The coating of the active component isgradually thinned at the edge of the sheet along a width 520. In theregion to the left of region 520, layers 106 are formed to their fullthickness. Thinning begins at a coating thickness transition region 525.An insulating plaster or coating is applied along region 530. The widthof the plaster (coated with insulating coatings) fully covers thethinning coating area on the conductive substrate and terminates in anarea that exposes the conductive substrate. The plaster/coating shouldbe electron or/and ion insulating, and capable of maintaining itsintegrity at high temperatures. One such coating is polyphenylenesulfide (PPS). Using this configuration reduces the possibility that ashort circuit will occur between the anode and cathode. Further,thinning the coating in the described manner reduces wrinkling that mayotherwise result from roller pressing a coating having a thick edge.

FIG. 7 is a cross-sectional view of one example of a coiled core 200. Ina coiled core, variable thicknesses and/or forces on the core 200 atopposed regions A and B may be problematic. To limit such problems, theanode sheet 105 and cathode sheet 110 terminate at opposed arcuateregions C and D instead of terminating at opposed planar regions A andB. As shown in FIG. 7, the anode sheet 105 terminates at 705 of region Cwhile the cathode sheet 110 terminates at 710 of region D. The separatorsheet 115 extends beyond the termination points 705 and 710 so that itwraps around to form the outer portion of the core 200. The separatorsheet 115 terminates at 715 along an arced side of the core 200. Thedirection in which the sheets are wound to form the core 200 isdesignated by arrow 720. In this structure, the cathode sheet 110 may belonger than the anode sheet 105.

In accordance with the construction of the core 200 shown in FIG. 7,regions A and B are substantially flat and do not have significantthickness variations. As a result, there is a reduction in wrinkles thatwould otherwise form through swelling of the core 200 during electrolytesoakage as well as during charging and discharging of the battery cell.Such wrinkles occur when the forces on the core 200 at regions A and Bare substantially non-uniform. By reducing this wrinkling, the lifespanof the core may be increased. Similarly, hidden safety issues caused bythe non-uniform charging or discharging of the core 200 are addressed(e.g., situations in which a wrinkled area of the core 200 produceslithium dendrites that cause a short inside the battery resulting in anexplosion).

FIG. 8 illustrates one embodiment of a bent connector 800 that may beused in the connection structure 325 of FIG. 4. Bent connector 800 isformed from a conductive material that is suitable for establishing anelectrical connection as well as a mechanical bond with the materialused to form connector 410 of FIG. 4 and preferably has a width that isat least 25% of the width W of the protective shell 305. The bentconnector 800 of FIG. 8 is generally Z-shaped and includes a first arm805 and second arm 810 that extend in opposite directions from atransverse portion 815. The second arm 810, as will be described below,extends from an interior to an exterior portion of the battery cellwhere it engages transverse portion 815. Transverse portion 815 ispositioned exterior to the battery cell where it electrically connectsthe second arm 810 with the first arm 805. First arm 805 effectivelyforms an electrical terminal of the battery that may be used to accessthe anode (or cathode) of the coiled core 200.

Bent connector 800 may include a weakening structure, such as groove820, which causes the bent connector 800 to break its electricalconnection with the core 200 under certain extraordinary forces, such asthose that occur when the vehicle is involved in an accident. In FIG. 8,a single groove 820 extends substantially along a width of thetransverse member 820. Additionally, or alternatively, groove 820 mayextend along a length of the first arm 805 exterior to the battery cell300 and/or along a portion of the second arm 810 exterior to the batterycell 300. Multiple weakening structures may also be used.

Depending on the electrical resistance characteristics of the materialforming the bent connector 800, the groove 820 may increase theresistance in an undesirable manner. In such instances, groove 820 maybe filled with a conductive material that is mechanically ductile. Anumber of materials are suitable for this purpose including, withoutlimitation, tin, conductive rubber, and other conductive ductilematerials. The resistance of the area having the groove 820 is thusdecreased while the overall safety characteristic that the groove ismeant to enhance remains.

FIG. 9 illustrates a further embodiment of a bent connector 900 that maybe used in the connection structure 325 of FIG. 4. Bent connector 900 isformed from a conductive material that is suitable for establishing anelectrical connection as well as a mechanical bond with the materialused to form connector 410 of FIG. 4. The bent connector 900 of FIG. 9is generally L-shaped and includes an arm 910 that extends from aninterior to an exterior portion of the battery cell where it engagestransverse portion 915. Transverse portion 915 is positioned exterior tothe battery cell. Transverse portion 915 effectively forms an electricalterminal of the battery that may be used to access the anode (orcathode) of the coiled core 200.

Bent connector 900 may include a weakening structure, such as groove920, which causes the bent connector 900 to break its electricalconnection in the region of the weakening structure. More particularly,the bent connector 900 breaks its electrical connection with the core200 when subject to certain extraordinary forces, such as those thatoccur when the vehicle is involved in an accident/collision. In FIG. 9,a single groove 920 extends substantially along a width of thetransverse member 915. Additionally, or alternatively, groove 820 mayextend along a length of the arm 910 at a portion of the arm 910 that isexterior to the battery cell. Multiple weakening structures may also beused.

Depending on the electrical resistance characteristics of the materialforming the bent connector 900, the groove 920 may increase theresistance in an undesirable manner. In such instances, groove 920 maybe filled with a conductive material that is mechanically ductile. Anumber of materials are suitable for this purpose including, withoutlimitation, tin, conductive rubber, and other conductive ductilematerials. The resistance of the area having the groove 920 is thusdecreased while the overall safety characteristic that the groove ismeant to enhance remains.

The dimensions of the grooves 820 and 920 of the bent connectors 800 and900 are dependent on the material used to form the connectors 800 and900. If the bent connector is formed from copper, the depth of thecorresponding groove may be approximately 50%-90% of the thickness ofthe transverse portion. The width of the groove along the transverseportion may be between about 100%-500% of the depth of the groove. Ifthe bent connector is formed from aluminum, the depth of thecorresponding groove may be approximately 30%-80% of the thickness ofthe transverse portion. The width of the groove along the transverseportion may be between about 100%-300% of the depth of the groove.

FIG. 10 shows how the bent connector of FIG. 8 may be used tointerconnect adjacent battery cells. As shown, a battery cell 300 a ispositioned adjacent battery cell 300 b for connection with one another.Battery cell 300 a includes an end cover structure 335 a. A bent cathodeconnector 800 a extends from an interior portion of the battery cell 300a where it is in electrical communication with the cathode collector ofthe corresponding coiled core (not shown). The transverse portion 815 aof the bent connector 800 a extends in a direction toward the adjacentbattery cell 300 b. Similarly, battery cell 300 b includes an end coverstructure 335 b. A bent anode connector 800 b extends from an interiorportion of the battery cell 300 b where it is in electricalcommunication with the anode collector of the corresponding coiled core(not shown). The transverse portion 815 b of the bent connector 800 bextends in a direction toward the adjacent battery cell 300 a.

The faces of the upstanding arms of connectors 800 a and 800 b arejoined with one another at junction 1005. Junction 1005 may be formed bywelding the faces together, bonding the faces with one another using anadhesive such as a conductive rubber, mechanically interconnecting thefaces with one another using a fastener, or similar joining structureand/or method. By interconnecting the bent connectors 800 a and 800 b atthe faces of the upstanding arms, a low resistance connection capable ofcarrying a high current is established between the cathode of thebattery cell 300 a and the anode of the battery cell 300 b. A similarstructure may be used at an opposite end of each battery cell 300 a and300 b to provide a low resistance connection capable of the carrying ahigh current between the anode of battery cell 300 a and the cathode ofthe battery cell 300 b with further adjacent cells to thereby connectall cells 300 with one another. In this manner, adjacent cells of abattery pack are electrically connected in series with one another.However, this interconnection architecture may also be used toelectrically connect adjacent battery cells in parallel with oneanother.

Both bent connector 800 a and 800 b include corresponding weakeninggrooves 820 a and 820 b. When either or both battery cells 300 a and/or300 b are jarred from their respective positions as a result of anaccidental impact with the vehicle, the material in the region of thegrooves 820 a and/or 820 b will fail and cause the battery cells 300 aand 300 b to electrically disconnect from one another. The safety of thebatteries used in the vehicle is enhanced in this manner.

FIG. 11 shows another structure for interconnecting adjacent batterycells 300 a and 300 b. The interconnection is substantially the same asshown in FIG. 10. However, bent connectors 800 a and 800 b are joined toone another using a fusing member 1105 disposed between the faces of theupstanding arms. The fusing member 1105 may be a tin/lead soldercomposition or similar material that melts and/or vaporizes underexcessively high electrical currents/temperatures that may occur duringa failure of battery cell 300 a, battery cell 300 b, and/or the batterysystem that includes battery cells 300 a and 300 b. To this end, thethickness, width, length, and composition of the fusing member 1105 isselected to result in electrical disconnection between the bentconnectors 800 a and 800 b when the electrical current and/ortemperature between them exceeds a predetermined critical value. Thesafety of the battery cells 300 a and 300 b when overcurrent and/ortemperature conditions are present is improved using thisinterconnection architecture.

FIGS. 35 and 36 show another structure for interconnecting adjacentbattery cells 300 a and 300 b. As shown, the connection structureincludes a first bent connector 800 a and a second bent connector 800 b.Each bent connector 800 a, 800 b includes a first arm 810 a, 810 b, atransverse portion 815 a, 815 b, and a further arm 805 a, 805 b. In theembodiment shown in FIGS. 35 and 36, arms 805 a and 805 b are shorterthan the corresponding arms of the connectors shown, for example, inFIGS. 8, 10, and 11. Bent connectors 800 a and 800 b may be joined toone another using a fusing member 1105 disposed between the faces of thearms 805 a and 805 b. The fusing member 1105 may be a tin/lead soldercomposition or similar material that melts and/or vaporizes underexcessively high electrical currents/temperatures that may occur duringa failure of battery cell 300 a, battery cell 300 b, and/or the batterysystem that includes battery cells 300 a and 300 b. To this end, thethickness, width, length, and composition of the fusing member 1105 isselected to result in electrical disconnection between the bentconnectors 800 a and 800 b when the electrical current and/ortemperature between them exceeds a predetermined critical value. Thesafety of the battery cells 300 a and 300 b when overcurrent and/ortemperature conditions are present is improved using thisinterconnection architecture.

The connectors 800 a, 800 b may also be adapted so that they break awayfrom one another when the interconnection structure is subject toexcessive forces that may occur during, for example, a vehicle impact.To this end, each transverse portion 815 a, 815 b includes a narrowedsection 3505 a and 3505 b. As shown, narrowed sections 3505 a and 3505 adefine open regions 3520. Open regions 3520 weaken the interconnectionstructure to facilitate disconnection of the connectors 800 a and 800 bunder excessive forces. Each arm 805 a and 805 b may have a width thatis substantially the same or otherwise corresponds to the width of thenarrowed sections 3505 a and 3505 b.

FIG. 37 shows another structure for interconnecting adjacent batterycells 300 a and 300 b. This interconnection structure is similar to theinterconnection structure shown in FIGS. 36 and 37. However, the arms805 a and 805 b extend in a direction toward battery cells 300 a and 300b.

FIG. 38 shows another structure for interconnecting adjacent batterycells 300 a and 300 b. In this interconnection structure, a first bentconnector 3800 a extends from battery cell 300 a while a second bentconnector 3800 b extends from battery cell 300 b. Each connector 3800 a,3800 b includes a first arm 3805 a, 3805 b that extends from therespective battery cell 300 a, 300 b and into engagement with arespective second arm 3810 a, 3810 b. Arms 3810 a and 3810 b extendtoward one another and overlap at a connection region 3815. Arms 3810 aand 3810 b may be adapted to disconnect from one another under excessiveforces, such as those that occur in a vehicle collision. To this end,one or both of arms 3810 a and 3810 b may include a weakening structure.In FIG. 38, the weakening structure comprises narrowed sections 3820 aand 3820 b formed in the overlapping portions of arms 3810 a and 3810 b.The narrowed sections 3820 a and 3820 b may be constructed as arcuateregions similar to the connection structures shown in FIGS. 35-37.

FIG. 39 shows another structure for interconnecting adjacent batterycells 300 a and 300 b. In this interconnection structure, a first bentconnector 3900 a extends from battery cell 300 a while a second bentconnector 3900 b extends from battery cell 300 b. Each connector 3900 a,3900 b includes a first arm 3905 a, 3905 b that extends from therespective battery cell 300 a, 300 b and into engagement with arespective second arm 3910 a, 3910 b. Arms 3910 a and 3910 b extendtoward one another and are engaged in an end-to-end manner at aconnection region 3915. Connection region 3915 may include a generallyV-shaped region that interconnects the arms 3810 a and 3810 b using amaterial that melts and/or vaporizes under temperatures that occur whenthe current flow between batteries 300 a and 300 b becomes excessivelylarge. The material in connection region 3915, for example, may be tinsolder or another material capable of mechanically and electricallyinterconnecting arms while melting and/or vaporizing at the desiredovercurrent temperature. Each connection arm 3900 a, 3900 b may includea weakening structure such as the one at 920 on the connector 900 shownin FIG. 9.

FIGS. 40 and 41 illustrate further interconnection structures thatinclude mechanically weakened regions that break the electricalconnection between batteries 300 a and 300 b at a predetermined locationunder excessive forces that occur, for example, during a vehicleaccident/collision. In FIG. 40, connector 4005 a is connected to batterycell 300 a while connector 4005 b is connected to battery cell 300 b.Transverse arms 4000 a and 4000 b terminate at respective arcuateportions 4010 a and 4010 b that join with one another at connectionregion 4015. The arcuate regions 4010 a and 4010 b are sufficientlystrong to facilitate mechanical and electrical interconnection betweenthe connectors 4005 a and 4005 b under normal operating conditions.However, the thinning of these material regions produces a weakenedconnection structure at which the connection between the transversemembers 4000 a and 4000 b is severed when subject to forces that occurduring a vehicle accident/collision.

In FIG. 41, connector 4105 a is connected to battery cell 300 a whileconnector 4100 b is connected to battery cell 300 b. Transverse arms4100 a and 4100 b overlap one another at region 4110 where theconnectors 4105 a and 4105 b are mechanically and electrically joinedwith one another. Each transverse arm 4100 a, 4100 b includes arespective arcuate region 4115 a, 4115 b at which the material formingthe transverse arm is thinned. The transverse arms 4100 a and 4100 b arealigned so that arcuate regions 4115 a and 4115 b overlie one another inconnection region 4110. The resulting structure is sufficiently strongto facilitate mechanical and electrical interconnection between theconnectors 4105 a and 4105 b under normal operating conditions. However,the thinning of the material regions at the joined arcuate regions 4115a and 4115 b produces a weakened connection structure at which theconnection between the transverse members 4100 a and 4100 b is severedwhen subject to forces that occur during a vehicle accident/collision.

FIG. 41A is a cross-sectional view through terminals 4100 a and 4100 btaken along section line 41A-41A of FIG. 41. In FIG. 41A, however, amultilayer clamp 4120 is disposed to engage arcuate regions 4115 a and4115 b. Clamp 4120 includes a first layer 4125 and second layer 4130having different thermal expansion characteristics. To this end, firstlayer 4125 may be an insulating material and have a higher coefficientof thermal expansion than second layer 4130. During an overcurrentcondition, the temperature of the terminals 4100 a and 4100 b increases.As the temperature increases, the first layer 4125 expands at a rategreater than the second layer 4130. Since the expansion of the firstlayer 4125 is constrained by the second layer 4130, the first layer 4125is driven against the thinned material sections at the arcuate regions4115 a and 4115 b. Ultimately, if the temperature exceeds apredetermined threshold value consistent with an overcurrent condition,the first layer 4125 exerts enough force against the arcuate regions4115 a and 4115 b to sever the connection between the terminals 4100 aand 4100 b.

FIGS. 42 through 46 show various manners in which terminals 4200 a and4200 b of adjacent battery cells 300 a and 300 b may be interconnectedwith one another. In each instance, the terminals 4200 a, 4200 b areinterconnected with one another using an electrically conductive bridgeconnector 4205. The bridge connector 4205 may take on a variety ofshapes including, but not limited to, a U-shape, an inverted U-shape, aZ-shape, an S-shape, or any other shape having one or more bendingangles between about 0° and 180°. The bridge connector 4205 may beformed as a single layered metal structure, multiple layer structure, oras a multiple layer metal foil. Forming the bridge connector 4205 as amultiple layer metal foil allows the bridge connector 4205 toadditionally function as a mechanical buffer that absorbs vibrationalenergy between the terminals 4200 a and 4200 b thereby increasing theintegrity of the overall terminal connection structure.

The bridge connector 4205 may be formed from a single metal material,multiple metal sheets having different thermal expansion coefficients,and/or from a memory alloy. Examples of materials having differentexpansion coefficients that may be used in a multiple metal sheetstructure include a Fe—Ni sheet combination, a Fe—Cu sheet combination,and/or a memory alloy/common metal combination. Memory alloys that maybe used in the bridge connector 4205 include Cu-based alloys and/orFe-based alloys. These include, without limitation, Cu—Zn—Al, Cu—Al—Ni,and/or Fe—Mn. The common metal may be, for example, Cu, Al, and/or Ni.

The bridge connector 4205 connects to face portions of the terminals4200 a and 4200 b. The effective welding surface between the bridgeconnector 4205 and a respective terminal may be about 0.5˜4 times thecross-sectional surface of the terminal. Solder having a lower meltingpoint than the metal of the connector and the terminal may be disposedat the junction between each end of bridge connector 4205 and therespective terminal. The connection between each terminal and the bridgeconnector 4205 may be formed through cold pressure welding, ultrasonicwelding, solder welding, flash welding, friction welding, resistancewelding, or the like. Preferably the connection is formed using solderwelding where the melting point of the alloy used in the solder has amelting temperature between about 150° C. and 250° C. Materials that maybe used include Sn, Au-20% Sn, lead-5% Sn, Ag—Sn and so on.

FIG. 42 shows a bridge connector 4205 having an inverted U-shape. Inthis embodiment, terminals 4200 a and 4200 b may have the generalcharacteristics of the terminals 800 a and 800 b shown in FIG. 10.Bridge connector 4205 may include first and second arms 4210 and 4215that are interconnected with one another by a transverse member 4220.First arm 4210 is connected to member 4225 of terminal 4200 a whilesecond arm 4215 is connected to member 4230 of terminal 4200 b. Bridgeconnector 4205 may be formed as a multilayered soft metal piece, such asfrom a multilayered copper foil. When the battery cells 300 a and/or 300b are subject to external forces, the transverse member 4220 may absorbthe generated impact stresses and protect the terminals from excessivewear and harm.

The bridge connector 4205 may be formed from a memory alloy or bimetalpiece. When the temperature of the interconnection structure elevatessuddenly due, for example, to an overcurrent or other abnormalcondition, the memory alloy or the bimetal piece may shrink in thedirection shown by arrows 4235 to withdraw itself from contact with eachof the terminals as the solder between the bridge/terminal junctionsmelts. As a result, the electrical and mechanical connection between theterminals 4200 a and 4200 b is broken to prevent the explosion of thebattery cells and/or other such dangerous consequences.

Memory alloys that may be used to construct bridge connector 4205include Cu based metal alloys and/or Fe based metal alloys, such asCu—Zn, Cu—Zn—Al, Cu—Al—Ni, or Fe—Mn—Si alloys. In connection with thestructure shown in FIG. 42, it is assumed that a Cu—Al—Ni alloy isemployed. In such instances, the bridge connector 4205 may be initiallyformed so that the angle between each arm 4210 and 4215 with respect totransverse member 4220 Is less than 90°. While in this shape, the bridgeconnector 4205 may be subject to a high-temperature treatment betweenabout 300-1000° C. for several minutes to impart a memory effect. Thebridge connector 4205 is then connected to terminals 4200 a and 4200 bin its normal assembled position. In this position, the angle betweeneach arm 4210 and 4215 is at an angle of about 90° with respect to thetransverse member 4220. The memory alloy will attempt to recover itsoriginal shape when the temperature of the bridge connector 4205 iselevated to a temperature commensurate with an overcurrent and/or otherabnormal battery cell operating condition.

FIG. 43 shows a bridge connector 4205 having an S-shape. In thisembodiment, terminals 4200 a and 4200 b may have the generalcharacteristics of the terminals 800 a and 800 b shown in FIG. 10.Bridge connector 4205 may include first and second arms 4305 and 4310that extend in opposite directions and that are interconnected with oneanother by a transverse member 4315. First arm 4305 is connected tomember 4225 of terminal 4200 a while second arm 4310 is connected tomember 4230 of terminal 4200 b. As above, the bridge connector 4205 maybe formed as a multilayer metal foil, bimetal piece, and/or memoryalloy. When formed from a memory alloy, bridge connector 4205 may havean original shape that corresponds to the shape required to disconnectit from contact with terminals 4200 a and 4200 b under elevatedtemperatures that occur during overcurrent and/or other abnormal batterycell operating conditions.

FIG. 44 shows a bridge connector 4205 having an inverted U-shape. Inthis embodiment, terminals 4200 a and 4200 b may have the generalcharacteristics of the terminals 800 a and 800 b shown in FIG. 10.Bridge connector 4205 may include first and second arms 4405 and 4410that are interconnected with one another by a transverse member 4415.First arm 4405 is connected to an exterior surface of member 4225 ofterminal 4200 a while second arm 4410 is connected to an exteriorsurface of member 4230 of terminal 4200 b. As above, the bridgeconnector 4205 may be formed as a multilayer metal foil, bimetal piece,and/or memory alloy. When formed from a memory alloy, bridge connector4205 may have an original shape that corresponds to the shape requiredto disconnect it from contact with terminals 4200 a and 4200 b underelevated temperatures that occur during overcurrent and/or otherabnormal battery cell operating conditions. In FIG. 44, the originalshape may be set so that the bridge connector 4205 expands in thedirections shown by arrows 4420 under such elevated temperatures.

FIG. 45 shows a bridge connector 4205 having a multilayer structure. Inthis embodiment, the bridge connector 4205 includes a first layer 4505that is disposed interior to arms 4225 and 4230 and a second layer 4510that is interior to and coextensive with the first layer 4505. Eachlayer 4505, 4510 has an inverted U-shape. Layer 4510 may be formed froma common metal while layer 4505 may be formed from a memory alloy. Thecommon metal layer 4510 and memory alloy 4505 may be bonded with oneanother so that changes in the shape of the memory alloy 4505 result incorresponding changes in the shape of the common metal layer 4510. Assuch, the bridge connector 4205 changes shape under elevatedtemperatures that occur during overcurrent and/or other abnormal batterycell operating conditions. This shape change causes the bridge connector4205 to disconnect terminals 4200 a and 4200 b from one another.

FIG. 46 shows a bridge connector 4205 having a multilayer structure. Inthis embodiment, the bridge connector 4205 includes a first layer 4605that is disposed exterior to arms 4225 and 4230 and a second layer 4610that is exterior to and coextensive with the first layer 4605. Eachlayer 4505, 4510 has an inverted U-shape. Layers 4610 and 4605 areformed from metals having different thermal expansion coefficients andmay be mechanically bonded to one another so that changes in the shapeof one layer will result in a corresponding change in the other layer.The difference in thermal expansion coefficients causes the bridgeconnector 4205 to change shape under elevated temperatures that occurduring overcurrent and/or other abnormal battery cell operatingconditions thereby disconnecting terminals 4200 a and 4200 b from oneanother. To further ensure that the terminals 4225 and 4230 areelectrically isolated from one another when the bridge connector 4205changes shape, an insulating layer 4615 may be disposed at an endportion of each arm 4225 and 4230 proximate the bridge connector 4205.

Battery cell interconnections such as those shown in FIG. 39 may includegravity enhanced overtemperature protection structures. An example ofone such structure is shown in FIGS. 47 and 48, where FIG. 47 is a topview of the structure and FIG. 48 is a side view of the structure. Thesefigures show the orientation of the terminals when the battery cells areturned on their sides in the manner shown in FIGS. 28A and 69 below.

In the embodiment shown in FIGS. 47 and 48, terminal 3900 a iselectrically connected to battery cell 300 a while terminal 3900 b iselectrically connected to battery cell 300 b. A conductive block 4705 issecured to the end portions of each terminal 3900 a and 3900 b using abonding material 4710. The conductive block 4705 extends along theentire width 4805 of connectors 3900 a and 3900 b as well as along theentire thickness 4715. The bonding material 4710 may be Sn-based solder,Bi-based solder, or Zn-based solder, but is preferably Sn-based. In oneexample, the solder may have a thickness of between about 0.3 mm and 1mm and, preferably between about 0.5 mm and 0.8 mm. The melting point ofthe solder material may be between about 100° Celsius and 450° Celsius.If the melting point is too low, the interconnection structure may notbe stable under ordinary operating conditions. If it is too high, themelting point may not be achieved during abnormal overtemperatureconditions. Sn-based solder is preferred since it has a melting point ofabout 231.9° Celsius.

The conductive block 4705 may be formed from a high density metal havinga melting point that is at least about 50° Celsius above the meltingpoint of the bonding material 4710. In this manner, the conductive block4705 may be securely fastened with terminals 3900 a and 3900 b using asuitable brazing technique. Such techniques may include inductionbrazing, iron soldering, resistance braze welding, or similar fasteningtechnique.

As shown in FIG. 48, the conductive block 4705 may have a trapezoidalshape in which the base portion 4810 is disposed at the lower portion ofthe connection structure. The conductive block 4705 is subject to theforce of gravity in the direction shown by arrow 4815. When theconnection structure is subject to overtemperature conditions such asthose that occur during overcurrent or other abnormal operation of thebattery system, the bonding material 4710 begins to melt. As the bondingmaterial melts, the conductive block 4705 moves downward in direction4815 under the influence of gravity. Ultimately, the conductive block4705 dislodges from engagement with the terminals 3900 a and 3900 bthereby severing the electrical and mechanical interconnection betweenthem.

Battery cell interconnections may also include overtemperatureprotection structures using electrical insulators that are dimensionedto expand the connection between the terminals when the temperature ofthe interconnection becomes excessive. FIGS. 49 through 51 illustratethree embodiments of such interconnections. In FIG. 49, the terminals4900 a and 4900 b are joined to one another by a bonding material 4710.The bonding material 4710 may be Sn-based solder, Bi-based solder, orZn-based solder, but is preferably Sn-based. In one example, the soldermay have a thickness of between about 0.3 mm and 1 mm. The melting pointof the solder material may be between about 100° Celsius and 450°Celsius, with a preference of about 232° Celsius. An expansion member4905 is disposed in the joint between the terminals 4900 a and 4900 b.As shown, the expansion member 4905 may have a circular cross-section,but other cross-sectional shapes may be used. Further, the expansionmember 4905 may be formed from an electrically insulating materialhaving a large thermal expansion coefficient. Still further, thematerial forming the expansion member 4905 may have a melting point thatsubstantially exceeds the melting point of the bonding material 4710.

When the interconnection structure is subject to an overtemperaturecondition, the bonding material 4710 begins to melt. Additionally, theexpansion member 4905 expands to drive arms 4910 a and 4910 b apart. Thecharacteristics of the bonding material 4710, expansion member 4905, andspacing between arms 4910 a, 4910 b are such that the expansion of theexpansion member 4905 drives the arms 4910 a and 4910 b apart asufficient distance to overcome the surface tension of the meltedbonding material 4710. The bonding material 4710 flows from the jointbetween the terminals and effectively severs the electrical connectionbetween the battery cells.

The interconnection shown in FIG. 50 is similar to the one shown in FIG.49. The principal difference between them is the shape of the terminals5000 a and 5000 b. More particularly, the terminals 5000 a and 5000 binclude inwardly extending arms 5005 a and 5005 b as opposed to theoutwardly extending arms 4910 a and 4910 b of terminals 4900 a and 4900b.

The interconnection structure shown in FIG. 51 is similar to the onesshown in both FIG. 49 and FIG. 50. The principal difference between themis the shape of the terminals. More particularly, the interconnectionshown in FIG. 51 includes a terminal 4900 a having an outwardlyextending arm 4910 a that is electrically connected with an inwardlyextending arm 5005 b of a terminal 5000 b. An electrically insulatingmember 5105 may be disposed between an end portion of arm 4910 a ofterminal 4900 a and transverse portion 5110 of terminal 5000. Theelectrically insulating member 5105 helps to ensure that terminals 4900a and 5000 b are electrically disconnected from one another when thebonding material 4710 melts and flows from the joint between arms 4910 aand 5005 b.

As described above, interconnection structures may include a bondingmaterial between the terminals that melts under the excessively hightemperatures that occur due to overcurrent conditions between thebattery cells 300 a and 300 b. Additionally, or in the alternative, theinterconnection structures may be provided with substructures thatrelease chemicals which interact with the joint between the terminals sothat the terminals are mechanically and electrically separated from oneanother under such excessively high temperature conditions. FIGS. 52 and53 show examples of these substructures as applied to theinterconnection structures shown in FIGS. 40 and 41, respectively.

In FIG. 52, connector 4005 a is connected to battery cell 300 a whileconnector 4005 b is connected to battery cell 300 b. Transverse arms4000 a and 4000 b terminate at respective arcuate portions 4010 a and4010 b that join with one another at connection region 4015. Connectionregion 4015 may include a bonding material such as solder. The arcuateregions 4010 a and 4010 b are sufficiently strong to facilitatemechanical and electrical interconnection between the connectors 4005 aand 4005 b under normal operating conditions. However, the thinning ofthese material regions produces a weakened connection structure at whichthe connection between the transverse members 4000 a and 4000 b issevered when subject to forces that occur during a vehicleaccident/collision.

One embodiment of a substructure which releases chemicals that interactwith the connection region 4015 is shown generally at 5205. In thisembodiment, the substructure 5205 includes an outer casing 5210 thatcontains a chemically reactive material 5215. The casing 5210 has agenerally circular cross-section and is adapted to fit within thearcuate regions 4010 a and 4010 b. Other cross-sectional shapes may beused depending on the particular structure of the terminals that areemployed. The casing material should meet several requirements. Forexample, the casing material should be capable of being bonded with thematerials of the arms 4005 a and 4005 b. Additionally, the casingmaterial should be non-reactive with the chemically reactive material5215. Further, the temperature at which the casing material begins tomelt should be close to the temperature generated during an overcurrentcondition. The casing material may be a synthetic resin, rubber,ceramic, or the like. Preferably, the casing is formed from a plasticand/or rubber compound having a melting temperature between 100° C. and350° C., depending on the overtemperature requirements. Such materialsmay include PP, PE, ABS, PPO, PPS, PTFE, and PEEK.

The chemically reactive material 5215 is preferably a liquid at theovercurrent temperature. It may or may not be a solid at normaloperating temperatures. For example, it may be an acidic or basicchemical solution that is reactive with the material at connectionregion 4015. Preferably, the chemical is a basic chemical including, forexample, NaOH.

Under normal conditions, the temperature of the arms 4000 a and 4000 bare below the melting point of any material at interconnection region4015 as well as below the melting point of the casing 5210 of thechemically reactive element 5205. As the temperature increases due to,for example, an overcurrent condition, the casing 5210 begins to melt.As the casing 5210 melts, the chemically reactive material 5215 isreleased and engages the materials of arms 4000 a and 4000 b as well asany material in interconnection region 4015. The released chemicalreacts with the material at interconnection region 4015, arm 4000 a,and/or arm 4000 b. The reaction is destructive and results in electricaldisconnection of the arms 4000 a and 4000 b from one another.

In FIG. 53, connector 4105 a is connected to battery cell 300 a whileconnector 4100 b is connected to battery cell 300 b. Transverse arms4100 a and 4100 b overlap one another at region 4110 where theconnectors 4105 a and 4105 b are mechanically and electrically joinedwith one another. Each transverse arm 4100 a, 4100 b includes arespective arcuate region 4115 a, 4115 b at which the material formingthe transverse arm is thinned. The transverse arms 4100 a and 4100 b arealigned so that arcuate regions 4115 a and 4115 b overlie one another inconnection region 4110. The resulting structure is sufficiently strongto facilitate mechanical and electrical interconnection between theconnectors 4105 a and 4105 b under normal operating conditions. However,the thinning of the material regions at the joined arcuate regions 4115a and 4115 b produces a weakened connection structure at which theconnection between the transverse members 4100 a and 4100 b is severedwhen subject to forces that occur during a vehicle accident/collision.

As in FIG. 52, the interconnection structure of FIG. 53 includes asubstructure 5205 which may release chemicals that interact with theconnection region 4110 under overtemperature/overcurrent conditions. Thesubstructure 5205 includes outer casing 5210 that contains thechemically reactive material 5215. The casing 5210 may have a generallycircular cross-section and be adapted to fit within the arcuate regions4115 a and 4115 b. Operation of the substructure 5205 with respect tothe region 4110 is substantially similar to the operation described inconnection with FIG. 52.

The interconnection structures shown in FIGS. 52 and 53 are based on ahorizontal alignment of the arms of the terminals connecting batteries300 a and 300 b. It will be recognized, however, that a substructure ofthe type generally shown at 5205 may be used in other interconnectionstructure orientations. In such alternate orientations, the substructure5205 is constructed and aligned with the terminals so that the reactivematerial 5215 is released to sever the electrical connection between theterminals. Still further, the substructure 5205 may be positioned on asingle one of the terminals to sever the electrical connection betweenthe terminals.

Overcurrent protection may also be based on the removal of a conductiveliquid between the terminals of battery cells 300 a and 300 b. Moreparticularly, the conductive liquid is present between the terminals ofthe battery cells 300 a and 300 b under normal operating conditions sothat the terminals are electrically interconnected with one another toconduct current. The conductive liquid is drained from between theterminals of the battery cells 300 a and 300 b when the temperature ofthe terminals is elevated due, for example, to an overcurrent conditionor other system fault.

FIG. 54 shows one embodiment of an overcurrent protection substructurebased on this principle. In this embodiment, terminal 5400 a isconnected to battery cell 300 a and terminal 5400 b is connected tobattery cell 300 b. Terminals 5400 a and 5400 b are mechanicallyisolated from one another at a separation region 5403. Electricalconnection between terminals 5400 a and 5400 b is established usinginterconnection substructure 5405. The interconnection substructure 5405includes a casing 5410 that holds a liquid conductor 5415 therein. Theliquid conductor 5415 establishes an electrical connection betweenterminal 5400 a and 5400 b in region 5403. Metals, metal alloys, andconductive solutions may be used as the liquid conductor 5415.Preferably, the liquid conductor 5415 is mercury or an Na—K alloy. Thecasing 5405 has a generally circular cross-section, but othercross-sectional shapes may be used depending on the particular structureof the terminals that are employed. The casing material may benon-reactive with the liquid conductor 5415. Further, the temperature atwhich the casing material begins to melt should be close to thetemperature generated during an overcurrent condition. The casingmaterial may be a synthetic resin, rubber, ceramic, or the like.Preferably, the casing is formed from a plastic and/or rubber compoundhaving a melting temperature between 100° C. and 350° C., depending onthe overtemperature requirements. Such materials may include PP, PE,ABS, PPO, PPS, PTFE, and PEEK.

Under normal conditions, the temperature of the arms 5400 a and 5400 bare below the melting point of the casing 5410, and the liquid conductor5415 is retained in region 5403 to facilitate current flow betweenterminals 5400 a and 5400 b. As the temperature increases due to, forexample, an overcurrent condition, the casing 5410 begins to melt. Asthe casing 5410 melts, the liquid conductor 5415 is released from thecasing 5410 and open circuits region 5403. Further current flow betweenbatteries 300 a and 300 b through terminals 5400 a and 5400 b ceases.

FIGS. 55 through 57B show a further embodiment of an interconnectionstructure in which overcurrent protection is based on the removal of aconductive liquid between the terminals of battery cells 300 a and 300b. In this embodiment, the overcurrent protection substructure, showngenerally at 5500, is constructed to operate with terminals that extendhorizontally from each battery cell. As shown, terminal 5400 a isconnected to and extends horizontally from battery cell 300 a. Terminal5400 b is connected to and extends horizontally from battery cell 300 b.Each terminal 5400 a and 5400 b extends from the respective battery intoa conduction chamber 5505 of the overcurrent protection substructure5500. A collection chamber 5510 is disposed below the conduction chamber5505. The conduction chamber 5505 and collection chamber 5510 are madefrom an insulating material such as plastic, rubber, ceramic, or thelike. During normal battery system operation, the conduction chamber5505 and collection chamber 5510 are sealed in a manner to preventleakage from one chamber to the other.

The protection substructure 5500 may be assembled in a number ofdifferent manners. FIG. 56 shows one such manner. In FIG. 56, thesubstructure 5500 is formed from two portions 5600 a and 5600 b. Portion5600 a is connected to and sealed with terminal 5400 a. Portion 5600 bis connected to and sealed with terminal 5400 b. Each portion 5600 a and5600 b includes half of the conduction chamber 5505 and half of thecollection chamber 5510. The portions 5600 a and 5600 b may be joinedwith one another using a hot melt connection, rubber connection,adhesive connection, welded joint, or the like. The portions 5600 a and5600 b may be sealed with the corresponding terminals 5400 a and 5400 busing injection molding, hot melting, adhesive bonding, penetrationagents sealing, or the like. The method used to join the portions to oneanother and to the terminals should be sufficient to prevent leakage ofany liquid from either the conduction chamber 5505 or the collectionchamber 5510.

FIGS. 57A and 57B are cross-sectional views through the protectionsubstructure 5500 during normal operation of the battery system. Duringnormal operation, a liquid conductor 5415 of the type described above iscontained within the conduction chamber 5505 and establishes anelectrical connection between terminal 5400 a and terminal 5400 b. Theliquid conductor 5415 may be injected into the conduction chamber 5505through an opening 5515 disposed at an upper portion of the conductionchamber 5505. Once the conduction chamber 5505 has been filled with thedesired amount of liquid conductor 5415, the opening 5515 may be closedwith a plug or other type of seal.

The conduction chamber 5505 is sealed from the collection chamber 5510to prevent leakage of the liquid conductor 5415 from the conductionchamber 5505 to the collection chamber 5510. FIG. 57B shows one mannerof sealing the conduction chamber 5505 from the collection chamber 5510.In this example, the conduction chamber 5505 terminates at a lowerchamber wall 5705 that separates the conduction chamber 5505 from thecollection chamber 5510. The lower chamber wall 5705 includes a flowopening 5715 that is normally sealed by a separation member 5720.Separation member 5720 may be made from a plastic and/or rubber materialhaving a melting temperature between about 100° C. and 350° C.,depending on the desired temperature at which the overcurrent protectionis to be activated. Suitable materials include, for example, PP, PE,ABS, PPO, PPS, PTFE, and/or PEEK.

During an overcurrent/battery failure condition, the temperature of theliquid conductor 5415 will increase. As the temperature reaches themelting point of the separation member 5720, the separation member 5720will become ineffective in sealing the conduction chamber 5505 from thecollection chamber 5510. The liquid conductor 5415 will flow from theconduction chamber 5505 to the collection chamber 5510 through the flowopening 5715. The flow may occur under the force of gravity and/or underthe force generated by an elevated pressure in the conduction chamber5505 (e.g., the force resulting from the overcurrent temperature of theliquid conductor 5415). As the liquid conductor 5415 exits theconduction chamber 5505, it will create an open circuit conditionbetween terminals 5400 a and 5400 b. In order to ensure that all of theliquid conductor 5415 drains from the conduction chamber 5505, thevolume of the collection chamber 5510 should be at least equal to orgreater than the volume of the conduction chamber 5505.

The protection substructure 5500 is easily manufactured and readilyrepaired/recycled. By collecting the liquid conductor 5415 in thecollection chamber 5510, it may be reused in a repaired or newprotection substructure 5500. This is particularly beneficial if theliquid conductor 5415 is not environmentally friendly. Additionally, theprotection substructure 5500 may be easily repaired by directing theliquid conductor 5415 back into the conduction chamber 5505 andreplacing the sealing member 5720.

FIGS. 58 through 60 show a still further embodiment of aninterconnection structure in which overcurrent protection is based onthe removal of a conductive liquid between the terminals of batterycells 300 a and 300 b. In this embodiment, the overcurrent protectionsubstructure, shown generally at 5800, is constructed to operate withterminals that extend vertically from the respective battery cell. Asshown, terminal 5800 a is connected to and extends vertically frombattery cell 300 a. Terminal 5800 b is connected to and extendsvertically from battery cell 300 b. Each terminal 5800 a and 5800 bextends from the respective battery into a conduction chamber 5805 ofthe overcurrent protection substructure 5800. A collection chamber 5810is disposed below the conduction chamber 5805. The conduction chamber5805 and collection chamber 5810 are made from an insulating materialsuch as plastic, rubber, ceramic, or the like. During normal batterysystem operation, the conduction chamber 5805 and collection chamber5810 are sealed in a manner to prevent leakage from one chamber to theother.

The protection substructure 5800 may be assembled in a number ofdifferent manners. FIG. 59 shows one such manner. In FIG. 59, thesubstructure 5800 is formed from two portions 5900 a and 5900 b. Portion5900 a is connected to and sealed with terminal 5900 a. Portion 5900 bis connected to and sealed with terminal 5800 b. Each portion 5900 a and5900 b includes half of the conduction chamber 5805 and half of thecollection chamber 5810. The portions 5900 a and 5900 b may be joinedwith one another using a hot melt connection, rubber connection,adhesive connection, welded joint, or the like. Further, the portions5900 a and 5900 b may be sealed with the corresponding terminals 5800 aand 5800 b using injection molding, hot melting, adhesive bonding,penetration agent sealing, or the like. The methods used to join theportions to one another and to the terminals should be sufficient toprevent leakage of any liquid from either the conduction chamber 5805 orthe collection chamber 5810.

FIG. 60 is a cross-sectional view through the protection substructure5800. During normal operation, a liquid conductor 5415 of the typedescribed above is contained within the conduction chamber 5805 andestablishes an electrical connection between terminal 5800 a andterminal 5800 b. The liquid conductor 5415 may be injected into theconduction chamber 5805 through an opening 5815 disposed at an upperportion of the conduction chamber 5805. Once the conduction chamber 5805has been filled with the desired amount of liquid conductor 5415, theopening 5815 may be closed with a plug or other type of seal.

The conduction chamber 5805 is sealed from the collection chamber 5810to prevent leakage of the liquid conductor 5415 from the conductionchamber 5805 to the collection chamber 5810. In FIG. 60, the conductionchamber 5805 terminates at a lower chamber wall 6005 that separates theconduction chamber 5805 from the collection chamber 5810. The lowerchamber wall 6005 includes a flow opening 6015 that is normally sealedby a separation member 6020. Separation member 6020 may be made from aplastic and/or rubber material having a melting temperature betweenabout 100° C. and 350° C., depending on the desired temperature at whichthe overcurrent protection is to be activated. Suitable materialsinclude, for example, PP, PE, ABS, PPO, PPS, PTFE, and/or PEEK.

During an overcurrent/battery failure condition, the temperature of theliquid conductor 5415 will increase. As the temperature reaches themelting point of the separation member 6020, the separation member 6020will become ineffective in sealing the conduction chamber 5805 from thecollection chamber 5810. The liquid conductor 5415 will flow from theconduction chamber 5805 to the collection chamber 5810 through the flowopening 6015. The flow may occur under the force of gravity and/or underthe force generated by an elevated pressure in the conduction chamber5805 (e.g., the force resulting from the overcurrent temperature of theliquid conductor 5415). As the liquid conductor 5415 exits theconduction chamber 5805, it will create an open circuit conditionbetween terminals 5800 a and 5800 b. In order to ensure that all of theliquid conductor 5415 drains from the conduction chamber 5805, thevolume of the collection chamber 5810 should be at least equal to orgreater than the volume of the conduction chamber 5805. FIGS. 12 and 13show a connection structure 1200 that may be utilized to bring the coreof battery cell 300 to an optimal operating temperature when the ambienttemperature falls below a predetermined threshold. Connection structure1200 includes a heating element 1205, such as a ceramic heater, that issecured to bent connector 800. A layer of a thermally conductivematerial 1210 is disposed between the bent connector 800 and the heatingelement 1205. Heating element 1205 may have an L-shaped cross-sectionand be dimensioned to conform with a surface of bent connector 800opposite the surface used to establish electrical contact with anadjacent battery cell. Layer 1210 may be formed from a material, such asa thermally conductive rubber, which serves as a conductive heatingelement, an electrical insulator, and/or as an adhesive between theheating element 1205 and the bent connector 800. Additionally, or in thealternative, bent connector 800 and heating element 1205 may be securedwith one another using a mechanical fastener that is formed from anelectrical insulator, such as PA66.

FIG. 13 shows a system that may be used to raise the temperature of thecore of battery cell 300 when temperature conditions indicate that thecore is at or may fall below a predetermined temperature threshold. Asshown, the system includes a temperature sensor 1305 that is disposed tomonitor a temperature associated with the need for core heating. Thetemperature sensor 1305 may be disposed to monitor the ambienttemperature of the vehicle, the ambient temperature of the batterysystem environment, the temperature of the battery cell 300, and/orother desired temperature. The temperature information is provided to acontrol system 1310. The control system 1310 uses the temperature sensorinformation to determine when the temperature detected by the sensor1305 falls below a predetermined threshold. When this occurs, thecontrol system 1310 directs electrical power to the heating element1205. The electrical power may be provided by a generator connected to agas powered engine of the vehicle and/or by a battery power system.Heating element 1205 responds to the electrical power by generating heatwhich is transferred through the layer 1210 to the bent connector 800.Bent connector 800, in turn, acts as a thermally conductive element thattransfers heat to the interior of battery cell 300 thereby raising thetemperature of the coiled core 200.

FIG. 14A shows one manner of connecting a multiple core structure 1450of a battery cell 300 to the bent connector 800. In this embodiment, themultiple core structure 1450 includes three separate cores that are eachconstructed in the manner of core 200. For the sake of simplicity, onlya single end of the battery cell 300 is shown, although the same basicstructure may be used for connecting the opposite end of the multiplecore structure 1450 with a corresponding end connector 800.

In FIG. 14A, multiple core structure 1450 is disposed within therectangular protective shell 305. An end cover assembly 335 engages withand seals an opening at the end of shell 305. A gasket 1405 formed froman electrically insulating material is disposed within the shell 305 andpositioned between the end of multiple core structure 1450 and the endcover assembly 335. Bent connector 800 extends into the interior of thebattery shell 305 through the end cover assembly 335 so that it isoffset from a centerline running longitudinally through the shell 305.

A plan view of the gasket 1405 is shown in FIG. 15. The gasket 1405includes three openings 1505, 1510, and 1515. Each opening is defined bya respective set of contoured elements disposed on each side of theopening. Opening 1505 is defined by contoured elements 1520 and 1525,opening 1510 by contoured elements 1525 and 1530, and opening 1515 bycontoured elements 1530 and 1535. Each contoured element includes arounded surface at a side proximate the coiled core 200 and a respectiveplanar surface opposite the rounded surface. Contoured elements 1525 and1530 are spaced from one another so that opening 1510 is larger thanopenings 1515 and 1520. As a result, the planar surface of contouredelement 1525 is positioned to facilitate protection of the core 200 inthe event that the bent connector 800 is driven toward the core 200under extraordinary forces, such as those that may occur during avehicle collision.

With reference again to FIG. 14A, current collector strips 1415 extendfrom the anode (or cathode) of each core 200 of the multiple corestructure 1450. Each current collector strip 1415 may be formed from oneor more foil layers, such as the foil layers forming the substratelayers of the anode (or cathode) of each core 200. Although each currentcollector strip 1415 is shown as a single foil layer, each currentcollector strip 1415 may also be formed from multiple foil layers thatare grouped with one another as they extend from the anode (or cathode)of each core 200 of the multiple core structure 1450. In FIG. 14A, thereare three current collector strips 1415 a, 1415 b, and 1415 c thatextend from the anode (or cathode) of a respective core 200 of themultiple core structure 1450. These current collector strips extendthrough respective openings 1505, 1510, and 1515 and into a cavity 1420of the gasket 1405. Within cavity 1420, each current collector strip1415 a, 1415 b, and 1415 c is electrically and mechanically bonded to arespective flexible connector foil 1425 a, 1425 b, and 1425 c. Variousconnection processes may be used to join the structures including,without limitation, ultrasonic welding, resistance welding, laserwelding, and/or another binding process.

As shown in Figure of 14A, the connector foils 1425 a, 1425 b, and 1425c are coiled within the cavity 1420 to join at a common side of the bentconnector 800. Connector foils 1425 b and 1425 c are coiled within afirst side of the cavity 1420 while connector foil 1425 a is coiledwithin a second side of the cavity 1420. The first side of the cavity1420 is larger than the second side of the cavity 1420 due to the offsetof the connector 800 with respect to the longitudinal centerline of theshell 305. Consequently, connector foils 1425 b and 1425 c have moreroom in which to coil around to fasten with the connector 800 thanconnector foil 1425 a. The angles at which the connector foils 1425 band 1425 c are bent, therefore, are relatively gradual. Gradual bendingangles are more desirable than drastic bending angles and are lesslikely to result in breakage of the corresponding connector foil.However, connector foil 1425 a is disposed in a smaller portion ofcavity 1420. As such, connector foil 1425 a may require a more drasticbend angle in order to coil around for connection to the connector 800.Drastic bending angles are subject to substantial mechanical and thermalfatigue and may result in breakage of the connector foil 1425 a.

In order to render the bending configuration of the connector foil 1425a more reliable, a coil guide member 1430 is bonded to the connectorfoil 1425 a. Coil guide member 1430 includes a bonding portion 1435 anda rounded portion 1440. The bonding portion 1435 is secured with theconnector foil 1425 a exterior to its connection with the otherconnector foils 1425 b and 1425 c. Rounded portion 1440 has a shape anddiameter that directs connector foil 1425 a to bend at a gradual angleas it approaches the bent connector 800 thereby increasing thereliability of the connector foil 1425 a. Further, coil guide member1430 may be dimensioned to drive the collector 1415 a and connector foil1425 a toward a side wall of the gasket 1405. In this manner, thecollector 1415 a and connector foil 1425 a do not experience as muchmovement as might otherwise occur when the battery cell 300 is vibrated.Similarly, the lengths of connector foils 1425 b and 1425 c may beselected so that the corresponding bending configuration limitsvibration of these components within the chamber 1420. The reliabilityand safety of the battery cell 300 is increased with such structures.

The use of the coil guide member 1430 may be extended to assemblieshaving more than three connector foils as well as assemblies having lessthan three connector foils. In each instance, the coil guide member 1430is preferably secured to a connector foil that bends on the side atwhich it is connected to bent connector 800 as opposed to a connectorfoil that coils below and around bent connector 800 for connection.Further, additional coil guide members may be secured with connectorfoils 1425 b and 1425 c to prevent unnecessary bending of theseconnector foils as well.

FIG. 14B shows one manner of connecting a core of a battery cell 300 tothe bent connector 800. In this embodiment, only a single core 200 isutilized. Accordingly, only a single current collector 1415 extends fromthe core 200 for electrical connection with the bent connector 800. Toreduce the degree of the angles that need to be formed in connectingfoil 1425 to reach bent connector 800, the current collector 1415 isdisposed through the opening 1515 that is furthest from the bentconnector 800. In all other respects, the end cover 300 of FIG. 14B isthe same as the one shown in FIG. 14A.

The gasket 1405 may include tabs 1410 that engage corresponding recessesin the protective shell 305. Tabs 1410 may be used to secure the gasket1405 in the shell 305. Additionally, or in the alternative, gasket 1405may be secured within the protective shell 305 through welding, one ormore mechanical fasteners, an adhesive, or other connection mechanism.

Gasket 1405 assists in protecting the core 200 in several differentways. For example, the portion of the gasket 1405 proximate the core 200helps maintain the core 200 in proper longitudinal alignment within theinterior of the protective shell 305. The offset contoured member 1525assist in preventing the connector 800 and the connections at its sideface from contacting the core 200 during an accident or mechanicalfailure. The narrowing of the openings provided by contoured members1520, 1525, 1530, and 1535 help guide current collectors 1415 a, 1415 b,and 1415 c into the chamber 1420 during the manufacturing of batterycell 300. Still further, gasket 1405 helps to stiffen the protectiveshell 305 to provide increased protection to the coiled core 200.

FIGS. 16 and 17 show one manner of sealing the end of protective shell305 with the end cover assembly 325. FIG. 16 is a cross-sectional viewthrough a transverse section of the end cover assembly 325 while FIG. 17is a cross-sectional view through a longitudinal section of the andcover assembly 325.

End cover assembly 325 includes a cover plate/end cap 1605, a scabbard1610, connector 800, and a sealing material 1615. To manufacture the endcover assembly 325, the cover plate 1605 and scabbard 1610 are welded toone another to form an integral structure. Without limitation, thewelding operation may include laser welding, argon arc welding, andother welding processes. The cover plate 1605 and scabbard 1610 may beformed from stainless steel. Once the cover plate 1605 and scabbard 1610have been welded to one another, they may be placed over the connector800 which extends from an interior portion of the battery cell to anexterior portion. End cover assembly 325 includes a cover plate 1605, ascabbard 1610, connector 800, and a sealing material 1615. Tomanufacture the end cover assembly 325, the cover plate 1605 andscabbard 1610 are welded to one another to form an integral structure.Without limitation, the welding operation may include laser welding,argon arc welding, and other welding processes. The manufacturingoperations that take place after the cover plate 1605 and scabbard 1610have been welded to one another are not heat intensive. Consequently,the likelihood that other components of the battery cell will sufferdamage as a result of the manufacturing of the end cover assembly 325 isreduced.

The cover plate 1605 and scabbard 1610 may be formed from stainlesssteel. Before further processing, the surfaces of the cover plate 1605,scabbard 1610, and connector 800 that will be contacted by the sealingmaterial 1615 may be abraded to increase adhesion between thesestructures and the sealing material 1615.

With reference to both FIGS. 16 and 17, the connector 800 includes upperchannels 1620 disposed on opposed faces of the connector 800 and lowerchannels 1625 disposed on opposed faces of the connector 800. The upperand lower channels 1620 and 1625 extend substantially along the lengthof connector 800. Channels 1620 are positioned so that they aregenerally juxtaposed to inwardly extending lips 1630 of the scabbard1610.

Connector 800 also includes a plurality of via holes 1635 that extendcompletely through the width of the connector. As shown in FIG. 16, thevia holes 1635 are positioned adjacent a further set of inwardlyextending lips 1640 of the scabbard 1610. As shown in FIG. 17, the viaholes 1635 may be disposed at various positions along the length of theconnector 800 and between the channels 1620 and 1625.

Once the cover plate 1605 and scabbard 1610 have been welded to oneanother, the connector 800 is directed to its desired position within aninterior channel of the scabbard 1610 and the sealing material 1615 isinjected into the interstitial regions between the connector 800,scabbard 1610, and cover plate 1605. The sealing material is injectedunder high pressure to fill channels 1620, 1625, via holes 1635, as wellas the regions around inwardly extending lips 1630 and 1640.

The sealing material 1615 may be a plastic (e.g., PFA, PES, PPS,modified PP, etc.), a rubber compound, a resin (e.g., an epoxy resin,phenol aldehyde modified epoxy resin, etc.), an agglutination rubber(e.g., a double component epoxy, hot melt rubber, etc.). The sealingmaterial 1615 should be an electrical insulator and be capable ofsustaining exposure to the electrolyte and hydrochloric acid. Further,the sealing material 1615 should be capable of bonding with the variousmetals used to form the connector 800, scabbard 1610, and cover plate1605 (e.g., copper, aluminum, stainless steel, and other metals).

The sealing material 1615 extends beyond the upper portion of thescabbard 1610. More particularly, the sealing material 1615 fills theinterior region between the scabbard 1610 and connector 800 and wrapsaround the outside of the scabbard 1610 to form a protective flange1645. The protective flange 1645 further enhances the integrity of theseal. Further, the protective flange 1645 may absorb some of thevibrational and impact forces that would otherwise be imparted to theconnector 800.

As shown in FIG. 61, the end cover assembly 325 may include a furtherprotection cover 6105 that generally conforms to the outermost portionsof other members of the end cover assembly 325. In the illustratedembodiment, protection cover 6105 includes a first portion 6115 thatextends along and conforms with an outer surface of the cover plate1605. Cover plate 1605 may include a cover plate flange 6120 thatengages a corresponding flange 6125 of the first portion 6115. Theprotection cover 6105 also includes a second portion 6110 that extendsat an angle of, for example, about 90° from the first portion 6115. Thesecond portion 6110 extends about and conforms with an outer surface ofthe scabbard 1610 and protective flange 1645, and terminates in anopening 6130 through which terminal 800 protrudes. Preferably, thesecond portion 6110 seals with the terminal 800 at the opening 6130.Still further, the second portion 6110 includes an interior flange 6140that engages the protective flange 1645. The region of the secondportion 6110 beneath the interior flange 6140 may be dimensioned so thatthe protective flange 1645 applies a force against the protection cover6105 to assist in securing the protection cover 6105 against the coverplate 1605.

The protection cover 6105 may be formed from an electrical insulator.For example, the protection cover 6105 may be formed from a plastic(e.g., PFA, PES, modified PP, or the like), rubber (e.g., EPDM,styrene-butadiene rubber, or the like), resin (epoxy resin, phenolicaldehyde modified epoxy resin, or the like). Such materials areinsulators, fire resistant, and are not readily degraded by theelectrolyte of the battery cell. By forming the protection cover 6105using insulating materials, short-circuits resulting from physicaldistortion of the connector 800 (e.g., during a vehiclecollision/accident) with respect to the cover plate 1605 are reducedand/or eliminated. Similarly, the protection cover 6105 may extend aboutthe edge portions of the cover plate 1605 to avoid undesired electricalcontact between the battery cell and other battery system structures.

Protection cover 6105 may be formed as an integral structure ormultipiece structure. FIGS. 62 and 63 illustrate multipiece protectioncover structures while FIG. 64 illustrates an integral protection coverstructure.

In FIG. 62, the protection cover 6105 is formed from two individualprotection cover halves 6200 a and 6200 b. Each half 6200 a and 6200 bincludes a respective first portion 6115 a, 6115 b that is dimensionedto extend along and conform with an outer surface of the cover plate1605. Each half 6200 a and 6200 b also includes a respective flange 6125a, 6125 b that engages the corresponding cover plate flange 6120. Secondportions 6110 a, 6110 b extend at an angle, for example, of about 90°from the first portions 6115 a, 6115 b. The second portions 6110 a, 6110b are dimensioned to extend about and conform with an outer surface ofthe scabbard 1610 and protective flange 1645. Openings 6130 a, 6130 bare disposed through each half 6200 a, 6200 b and are dimensioned toallow terminal 800 to protrude therethrough. Second portions 6110 a,6110 b include interior flanges 6140 a, 6140 b that engage theprotective flange 1645. Protective flange 1645 may apply a force againstthe interior flanges 6140 a, 6140 b to assist in securing the protectioncover 6105 against the cover plate 1605.

The protection cover halves 6200 a, 6200 b are joined with one anotherusing mating structures. In FIG. 62, half 6200 a includes a rectangularextension 6205 a that is dimensioned to engage rectangular opening 6205b of half 6200 b. In applying the protection cover 6105 to the end coverassembly 325, halves 6200 a and 6200 b may be directed laterally towardone another so that the interior flanges 6140 a and 6140 b engage anunderside of the protective flange 1645. Concurrently, the matingstructures 6205 a and 6205 b are directed toward one another until theyare substantially or fully engaged. Depending on the dimensions andcharacteristics of the protection cover 6105, a bonding agent may beapplied to an exterior surface of each of the mating structures 6205 aand 6205 b prior to assembly to increase the overall integrity of theprotection cover 6105. Other bonding techniques may also be used.

The mating structures may take on a variety of different shapes. In FIG.63, half 6200 a includes an oval extension 6305 a that is dimensioned toengage a corresponding oval opening 6305 b of half 6200 b. Other matingstructure shapes (e.g., triangular, trapezoidal, or the like) may alsobe used.

In FIG. 64, the protection cover 6105 is formed as a singular,integrated structure. When formed in this manner, the protection covermaterial is preferably highly elastic so that the protection cover maybe applied to the end cover assembly 325 over terminal 800.

The protection cover 6105 may include visual indicia indicative of thecharacteristics of the battery cell/terminal. In the protection coversshown in FIGS. 62-64, a visual indicator 6215 of the pole type isprovided to identify the corresponding terminal as a cathode terminal oranode terminal. The exemplary indicator 6215 identifies thecorresponding terminal 800 as a cathode terminal.

With reference to FIG. 17, the end cover assembly 325 includes a blowout vent 1800. The blow out vent 1800 is adapted to prevent acatastrophic rupture of the battery cell 300 in the event that theinterior pressure of the battery cell 300 reaches an unsafe level. Ifthis pressure is not relieved, the battery cell 300 may explode. In eachof FIGS. 62 through 64, the protection cover 6105 includes an exhaustvent 6210 that overlies the blow out vent 1800 so that the protectioncover does not prevent the release of gases and/or other materials fromthe blow out vent 1800.

FIG. 18 shows one embodiment of a blow out assembly 1800 that may beused on the end cover assembly 325. Blow out assembly 1800 includes avent cover 1805, a rupture pin 1810, and a vent base 1815. As shown, theblow out assembly 1800 is secured over an exhaust vent 1820 of the coverplate 1605.

The vent cover 1805 may be in the form of a truncated trapezoidal conewith an exposed bottom surface. A plurality of exhaust openings 1825 aredisposed through the sides of the vent cover 1805. The cumulative areaof the exhaust openings 1825 should be greater than the area of opening1820. The rupture pin 1810 extends through an opening at the top of thevent cover 1805 where it is secured using, for example, spot laserwelding.

The vent base 1815, as shown in both FIGS. 18 and 19, includes anannular ring 1830 and a flange 1835. A deformable membrane 1840 isattached to the annular ring 1830 by welding it over the interioropening of the ring. The width of the annular ring 1830 has a diameterthat is preferably less than about 70% of the width of its interioropening. Further, the width of lip 1845 of the annular ring 1830preferably does not exceed 70%-80% of the width of the exhaust vent1820.

The deformable membrane 1840 is preferably formed from the same materialas the cover plate 1605 (e.g. aluminum, stainless steel, etc.) and has athickness between about 0.01 mm-0.1 mm, with a preferable thicknessbetween 0.01 mm and 0.05 mm. The thickness of the deformable membrane1840, however, may be adjusted based on the overpressure level at whichthe vent assembly 1800 is to fail. The deformable membrane 1840 may bebrazed to properly seal over the opening of the annular ring 1830 andmay be formed from a metal foil, such as aluminum foil, copper foil,etc.

Valve base 1815 is welded to the cover plate 1605 using a high energybeam such as a laser or electronic beam. The vent cover 1805 includes aboss 1850 that is secured with vent base 1815. Boss 1850 includes aplurality of openings 1855 that are distributed about its circumferenceto facilitate a high energy beam welding of the vent cover 1805 to thevent base 1815.

As the pressure within the battery cell 300 approaches a critical level,the deformable membrane 1840 distorts in the direction of the rupturepin 1810. Upon reaching the critical pressure, the deformable membrane1840 is pierced by the rupture pin 1810 to release the pressure andpreventing explosion of the battery cell 300. The pressure at whichrupture of the deformable membrane 1840 occurs can be adjusted byadjusting the distance between the deformable membrane 1840 and therupture pin 1810. Further, the shape of the rupture pin 1810 may be usedto cause different rupture modes under different critical pressures.Still further, during assembly of the battery cell, when the air withinthe battery cell 300 is exhausted during manufacturing, there is areverse distortion of the deformable membrane 1840 that increases thedistance between the membrane and the rupture pin 1810. Thischaracteristic facilitates rapid manufacture of normal batteries andsafe removal of abnormal batteries from the production line.

FIGS. 21 and 22 show alternative pressure relief structures 2100 and2200. Each structure may be disposed sealed with a corresponding exhaustopening of the cover plate 325. Relief structure 2100 is formed from adeformable membrane 2105 having a weakening groove 2110. Similarly,relief structure 2200 is formed from a deformable membrane 2205 having aweakening groove 2210. The principal differences between structures 2100and 2200 are in the shape formed by the edges of each membrane and theshape of the weakening groove disposed in each membrane. The dimensionsof the deformable membranes 2105 and 2205 of each pressure reliefstructure 2100 and 2200 as well as the depth and extent of eachweakening groove 2110 and 2210 are dependent on the particular pressureat which the respective structure is to fail to prevent explosion of thebattery cell. A still further alternative pressure relief structureincludes filling the exhaust vent with a polymer sealing material, wherethe polymer seal is adapted to fail above a predetermined pressure.

FIGS. 65-67 illustrate a further embodiment of a blow out vent 1800.FIG. 65 shows the blow out vent 1800 in an assembled state on the coverplate 1605. FIG. 66 is an exploded view of the blow out vent 1800 whileFIG. 67 is a cross-sectional view of the vent.

In this embodiment, blow out vent 1800 includes a membrane 6605 that isdisposed over a trough 6610 that, in turn, surrounds an exhaust opening1820 of cover plate 1605. The trough 6610 includes an interior edge 6625defining opening 1820 and an outer edge 6620 defining the periphery ofthe trough 6610. The radial difference between edges 6620 and 6625 maybe about 10% to 15% of the radius of exhaust opening 1820.

Membrane 6605 is dimensioned to fit snugly within the outer edge 6620 ofthe trough 6610. A variety of materials may be used to form the membrane6605 including, for example, aluminum, aluminum alloy, steel, or anyother material that satisfies the material failure requirements for thevent 1800. Further, the material may be selected so that it is one whichmay be easily welded. The thickness of the material may be between about0.01 mm and 0.1 mm. Although the illustrated membrane 6605 is circular,other shapes (e.g., rectangular, elliptical, square, or the like) mayalso be used.

A safety mask 6615 is disposed over membrane 6605. The safety mask 6615includes a rim 6630 that fits snugly with outer edge 6620 of trough6610, where it is welded to the outer edge 6620 at one or more joints6705. Welding techniques that may be used include, for example, laserwelding and/or electron beam welding.

A crown portion 6635 extends from rim 6630 in a direction away frommembrane 6605. The crown portion 6635 may have a radius that isgenerally equal to the radius of the opening 1820. A plurality ofoval-shaped openings 6640 are disposed in the sidewalls of the crownportion 6635. The total area of the oval-shaped openings 6640 may beapproximately equal to or greater than the area of opening 1820. Thewall thickness of the safety mask 6615 may be between about 0.1 mm-0.5mm.

The foregoing blow out vent structure may be used to achieve numerousadvantages. For example, assembly of the structure is both simple andeconomical. When the membrane 6605 and safety mask 6615 are assembledover the opening 1820, the assembly may be easily secured with the coverplate 1605 by welding the rim 6630 of the safety mask 6615 to the outeredge 6620 of the trough 6610. Safety mask 6615 assists in protectingmembrane 6605 from external forces thereby ensuring the integrity of theoverall blow out vent 1800. Still further, the safety mask 6615 may beused to reduce the expulsion of non-gaseous materials from the batterycell when the interior pressure of the battery cell exceeds safe levels.

FIG. 23 is a block diagram of a battery pack 2300 in which multiplebattery cells 300 are interconnected with one another in series andgrouped within a single housing 2305. The number of battery cells 300 ina single housing 2305 may range from 8 to 15, with 10 battery cells perpack being preferable. Terminal connectors 2810 are disposed at oppositeends of the battery pack 2300 and are used to provide a means forestablishing an electrical and mechanical connection between multiplebattery packs 2300. Housing 2305 is preferably hermetically sealed andwater-tight, but includes ducts 2310 to receive a flow of a thermalfluid therethrough. The ducts 2310 are disposed laterally on oppositesides of the battery pack 2300 so that the flow of thermal fluid runsproximate the connectors 800 to either heat or cool the battery cells300 of the battery pack 2300. The protective shells of adjacent batterycells may be proximate one another in that they are in direct contactwith one another or disposed immediately adjacent one another atopposite faces of an insulator sheet.

FIG. 24 is an exploded view of one embodiment of a housing 2305 that maybe used to form battery pack 2300. In this embodiment, housing 2305includes a plurality of series connected battery cells 300. The batterycells 300 are connected with one another in the manner shown in FIG. 23.A separator 2405 made from an insulating material is disposed betweeneach battery cell 300 to electrically isolate the protective shells ofthe battery cells 300 from one another. Preferably, however, theseparators 2405 are not employed. Rather, the protective shells arepreferably in direct contact with one another so that they form a singlethermal unit. Temperature control is thereby more easily maintained.

Battery cells 300 are disposed between a bottom plate 2410 and a topplate 2415 to limit movement of the battery cells 300 along the y-axis.Baffle structures 2420 are disposed on each side of the group of batterycells 300 and oriented to traverse the length of the battery cells 300.The baffle structures 2420 cooperate with one another to limit movementof the battery cells 300 along the x-axis. Side plates 2425 are disposedat opposite ends of the battery cells 300 and extend along the width ofthe battery cell group. The side plates 2425 limit motion of the batterycells 300 along the z-axis.

Sealing elements 2450 may be located between each baffle structure 2420and the top and bottom plates 2415, 2410 as well as between each sideplate 2425 and the top and bottom plates 2415, 2410. In this manner, thetop and bottom plates 2415, 2410 form water-tight seals with the matingcomponents. Such seals assist in preventing short circuits that wouldotherwise result when a battery cell 300 fails and allows liquid toescape.

The baffle structures 2420 are made of an insulating plastic materialhaving the desired mechanical strength, thermal degradation resistance,low temperature ductility, and resistance to battery and environmentalchemicals in the vehicle. One embodiment of a baffle structure 2420 isshown in FIG. 25. Each baffle structure 2420 is comprised of a baffleplate 2430, a baffle stiffener 2435, and apertures 2440 disposed at thecorners of the baffle structure 2420. Apertures 2440 are adapted toaccept corresponding tension rods that extend between the bafflestructures 2420 to secure the battery cells 300 therebetween. The totalthickness of each baffle structure 2420 may be between about 3 mm and 15mm. The thickness of each baffle plate 2430 may be between about 3 mmand 5 mm. The thickness of each baffle stiffener 2435 may be betweenabout 5 mm and 2 mm. The baffle stiffener 2435 evenly distributeshorizontal and vertical forces throughout the baffle structure 2420 andincreases the ability of the baffle structure 2420 to protect thebattery cells 300. Via holes may be pre-positioned to facilitate the useof mechanical fasteners, such as screws, at the four corners of thebaffle structure 2420. Such mechanical fastening is convenient forconnecting the top and bottom plates 2415, 2410 to the baffle structure2420. There are L-shaped structures on the baffle structure 2420 thatare positioned to mate with the top and bottom plates 2415, 2410. Thetop plate 2415 is located between an upper L-shape structure and a lowerL-shape structure of the baffle structure 2420. An aperture is locatedbetween the top plate 2415 and the upper L-shaped structure of thebaffle structure 2420. The aperture is adapted to receive a pin whichlimits movement between the top plate 2415 and the baffle structure 2420thereby inhibiting movement of the battery cells 300 along the x-axisand y-axis.

The top and bottom plates 2415, 2410 are made from a plastic insulatormaterial having the desired mechanical and chemical characteristics. Asshown in FIG. 26, the top and bottom plates 2415, 2410 are eachcomprised of a flat plate 2605, a stiffener 2610, and apertures 2615.The apertures 2615 are adapted to receive corresponding tension rodsthat extend between the top and bottom plates 2415, 2410. The wholethickness of each of the top and bottom plates 2415, 2410 may be betweenabout 3 mm and 15 mm. The thickness of each flat plate 2605 may bebetween about 3 mm and 5 mm. The thickness of each stiffener 2610 isbetween about 5 mm and 10 mm. The stiffener 2610 is adapted todistribute horizontal and vertical forces evenly over the respective topand bottom plate structures 2415, 2410. Pre-embedded bolts on the topand bottom plates 2415, 2410 are used to connect the top and bottomplates 2415, 2410 with the baffle structures 2420 as well as with theside plates 2425. A boss at the inner side of the top plate 2410 limitsmotion of the battery cells 300 along the y-axis.

The side plates 2410 are made of plastic insulator material having thedesired mechanical and chemical characteristics. As shown in FIG. 26,each side plate 2425 has an outline that matches the side openingsformed when the top plate 2415 and bottom plate 2410 are connected withone another.

The battery pack housing 2305 is advantageous for several reasons. Forexample, the battery pack housing 2305 limits movement of the batterycells 300 along every motion excess thereby improving the reliability ofthe battery pack 2300 and prolonging the battery service life. Themovement of the battery cells 300 may be readily limited along each axisby designing the baffle structures 2420 and the top and bottom plates2415 in a manner which decreases the volume occupied by the battery pack2300. By forming the housing 2305 from an insulating material, the riskof short-circuits is reduced because the battery cells 300 cannotelectrically connect with each other through the housing 2305. Further,by using a plastic material to form the components of the housing 2305the weight of the battery pack 2300 is reduced. Still further, thelikelihood that short-circuits will result from battery cell leakage isreduced since a sealing material is provided at the joints between thevarious components of the battery pack 2300 thereby preventing fluidleakage from the battery pack

FIG. 27 shows a connector 2700 that is used to mechanically andelectrically interconnect adjacent battery packs 2300. Connector 2700includes a first conductive arm 2705 and a second conductive arm 2710that are connected by an arch-shaped, multilayer metal foil 2715. Thearch-shaped foil 2715 may have a thickness between about 0.01 mm and 5.0mm and may be formed from copper foil to make it convenient for welding.Alternatively, conductive arms 2705 and 2710 as well as the arch-shapedfoil 2715 may be formed from nickel, aluminum, or other metal.Preferably, conductive arms 2705, 2710 and arch-shaped foil 2715 aremade from the same material to increase the overall conductivity of theconnector 2700. Formation of the arch-shaped foil 2715 may include hotpressing a plurality of thin metal sheets to one another while forgingthem into an arch-shaped structure. Each conductive arm 2705 and 2710includes an L-shaped joint 2720 proximate the arch-shaped foil 2715 atwhich the arch-shaped foil 2715 is welded and/or hot pressed to therespective arm. The size of each conductive arm 2705, 2710 andarch-shaped foil 2715 is determined by the size of the electrodeterminals of the battery packs that use connector 2700 as well as thecurrent carrying capacity needed between the battery packs. Thearch-shaped foil 2715 may be dimensioned so that it fails when subjectto an impact force that exceeds a predetermined magnitude to therebydisconnect the battery pack from an adjacent battery pack. Stillfurther, the arch-shaped foil 2715 may be dimensioned to function as afuse to disconnect adjacent battery packs when the current between theadjacent battery packs exceeds a predetermined level.

FIG. 68 shows a further connector 2700 that may be used to mechanicallyand electrically interconnect adjacent battery packs 2300. In thisembodiment, connector 2700 includes a first conductive arm 6805 and asecond conductive arm 6810 that are connected by an arch-shaped metalmember 6815. The arch-shaped metal member 6815 may be formed as a metalmesh 6825 that extends between opposed arch-shaped support arms 6830.The metal mesh 6825 may have a thickness between about 0.01 mm and 5.0mm and may be formed from strands of a single type of metal or multiplemetals to make it convenient for welding. Arms 6805, 6810 may be formedas metal sheets having openings 6820 through which fasteners extend tosecure the connector 2700 to the respective battery packs. Conductivearms 6805 and 6810 as well as the arch-shaped metal member 6815 may beformed from copper, nickel, aluminum, or other metal. Preferably,conductive arms 6805, 6810 and arch-shaped metal member 6815 are madefrom the same material to increase the overall conductivity of theconnector 2700. The size of each conductive arm 6805, 6810 andarch-shaped metal member 6815 is determined by the size of the electrodeterminals of the battery packs that use connector 2700 as well as thecurrent carrying capacity needed between the battery packs. Thearch-shaped metal member 6815 may be dimensioned so that it fails whensubject to an impact force that exceeds a predetermined magnitude tothereby disconnect the battery pack from an adjacent battery pack.Further, the arch-shaped metal member 6815 may be adapted to function asa fuse to disconnect adjacent battery packs when the current between theadjacent battery packs exceeds a predetermined level. Still further,connector 2700 may be formed so that it is sufficiently elastic tomechanically buffer any motion between adjacent battery packs.

FIG. 28 shows how connectors 2700 are used to interconnect multiplebattery packs 2805 a and 2805 b that are arranged in a head-to-headconfiguration. However, the battery packs 2805 a and 2805 b may also bearranged in a side-to-side manner as shown in FIG. 69 and still useconnectors 2700. As shown, battery packs 2805 a and 2805 b each have apair of battery pack terminals disposed along a single side of the pack,one terminal at each end of the side. The battery pack terminals may beadapted to break when subject to the extraordinary forces that occurduring a vehicle accident or the like. A connector 2700 is used at eachend of the battery pack to establish a mechanical as well as electricalconnection between the battery pack terminals. For simplicity, onlyterminals 2810 a and 2810 b are shown and discussed, although the sameconfiguration is used between each terminal of a battery pack that isadjacent a terminal of another battery pack. The connector 2700 betweenthe batteries packs 2805 a and 2805 b provides a mechanical buffer thatabsorbs impact forces when there is a relative displacement between thebattery packs 2805 a and 2805 b. Still further, the connector 2700 maybe adapted to sever the connection between adjacent battery packs whensubject to the extraordinary forces that occur during a vehicle accidentor the like.

The connector 2700 is secured to the battery packs 2800 a and 2800 b byconnecting the conductive arm 2710 to a connection plate 2830 a ofterminal 2810 a and the conductive arm 2705 to a connection plate 2830 bof the adjacent terminal 2810 b. Each conductive arm 2705 and 2710includes a groove 2725 adapted to receive a welding wire (see FIG. 27).Further, each arm 2705, 2710 includes a plurality of apertures 2730adapted to receive mechanical fasteners. To connect the adjacentterminals of the battery packs 2805 a and 2805 b, a welding wire isplaced in each groove 2725. Each arm 2705, 2710 is then welded (e.g.,using brazing, laser welding, ultrasonic welding, etc.) to thecorresponding terminal. Preferably, each arm is attached to thecorresponding terminal using brazing. Brazing allows easy maintenance ofthe interconnection between the battery packs and, further, simplifiesreplacement of a battery pack in the battery system since the metalalloy forming the interconnection may be easily reheated to separate thebattery pack from other battery packs in the battery system.Additionally, mechanical fasteners 2840, such as screws, bolts, or thelike, are inserted into apertures 2715 to engage corresponding aperturesof the respective terminal and establish a more reliable connectionbetween the conductive arm and corresponding terminal. Welding andsecuring the connector 2700 to the corresponding terminals of adjacentbattery packs in this manner establishes a low resistance, high currentcapacity path between the adjacent battery packs. Although the adjacentbattery packs may be connected so that they are electrically parallelwith one another, the preferred arrangement is to have them connectedserially.

FIG. 29 shows a battery system 2900 that supplies electrical power toand receives electrical power from a motor/generator of a vehiclecapable of being driven by electric power. Battery system 2900 includesmultiple battery packs 2805. The number of battery packs may be aboutfive, and preferably ten. Each battery pack 2805 includes a plurality ofcells 300, preferably in a range between 8 and 15 packs, and, morepreferably, ten packs. The cells 300 of each battery pack 2805 areelectrically connected in series with one another. Further, the multiplebattery packs 2805 are electrically connected in series with oneanother.

Each battery pack 2805 is disposed in a respective battery pack housing2305. The vehicle is provided with a compartment containing the multiplebattery packs and their housings. The compartment facilitates electricalconnection to the motor/generator. The battery pack housing 2305 foreach battery pack 2805 is substantially sealed from the ambientenvironment (e.g., water-tight) with the exception that openings areprovided through each battery pack 2805 in a region proximate theirrespective terminals. The openings of adjacent battery pack housings2305 are interconnected by duct work to facilitate circulation of acooling fluid, such as air, throughout the battery system 2900.

The compartment containing battery system 2900 may be shaped and sizedto fit partially under a rear passenger seat of the vehicle andpartially in a trunk compartment of the vehicle. Alternatively, thecompartment may be shaped and sized to fit under a floor of the vehicle.

In FIG. 29, a thermal fluid, such as air, is driven through the batterysystem 2900 by a pump 2905. The pump 2905 drives the thermal fluidthrough the system 2900 in the directions designated by the flow arrows2910. As illustrated by the flow arrows, the pump 2905 directs thethermal fluid through a thermal processing unit 2915 before it isprovided to an entrance 2927 of a central duct 2930 for distribution toother portions of the system 2900. The thermal processing unit 2915 mayinclude a condenser 2920 to cool the thermal fluid and a heater 2925 toheat the thermal fluid. The condenser 2920 is activated when thetemperature of the battery system 2900 exceeds a predeterminedthreshold. Likewise, the heater 2925 is activated when the temperatureof the battery system 2900 falls below a predetermined threshold.

As the thermal fluid circulates through the central duct 2930, it eitherheats or cools the terminal portions of each battery pack 2805 proximatethe central duct 2930. Upon reaching an end portion 2940 of the ductwork, the thermal fluid is directed toward the exterior ducts 2910, 2940of the battery system 2900. This allows the thermal fluid to either heator cool the terminal portions of each battery pack 2805 proximate theexterior ducting of the battery system 2900. The battery cells 300within the battery system 2900 thus operate in a controlled environmentin which the temperature is maintained at an optimal level. Some of thethermal fluid may be channeled from the ducts of the battery system 2900to the passenger compartment of the vehicle. In this manner, the heatgenerated by the battery system 2900 is used to heat the interiorpassenger compartment of the vehicle. The amount of thermal fluidchanneled from the ducts of the battery system 2900 may be controlled byan individual within the passenger compartment to regulate thecompartment temperature.

FIGS. 30 through 34 illustrate advantages associated with providingconnections to the anode and cathode of a coiled core at opposite endsof the core. For comparison, FIG. 30 shows a battery 3000 having a core3005, an anode connector 3010, and a cathode connector 3115. The anodeconnector 3010 and cathode connector 3015 are positioned at the sameside of the core 3005. The current distribution in the core 3005 duringoperation is indicated by shading. As shown, there is a substantialcurrent density proximate the connectors 3010 and 3015. Areas of highcurrent density are associated with elevated temperatures in accordancewith Ohm's law. Consequently, the areas proximate connectors 3010 and3015 run hot during operation and degrade the performance of thebattery. The longevity of the battery 3000 is also impacted.

FIG. 31 shows a battery 3100 having a coiled core 3105, an anodeconnector 3110, and a cathode connector 3115. The anode connector 3110and cathode connector 3115 are disposed at opposite sides of the coiledcore 3105. The core 3105 has a length 3120 and a width 3125. Anodeconnector 3110 has a width 3130 while cathode connector 3115 has a width3135. Although width 3130 and 3135 are shown as being less than thewidth 1025, these widths may be extended so that they are substantiallycommensurate with the width 3125 of the core 3105.

The dimensions shown in FIG. 31 may take on various proportions. Forexample, the ratio of length 3120 with respect to width 3125 may bebetween about 1.5 to 4.5, with a preference between about 2.5 and 3.5.The ratio of width 3130 with respect to width 3135 may be between about0.8 and 1.2, with a preference between 0.9 and 1. The ratio of the width3130 (as well as the width 3135) with respect to the width 3125 may bebetween about 0.3 and 0.6, with a preference between 0.4 and 0.5.

FIG. 32 illustrates a situation in which the width 3130 and width 3135are approximately the same. In this situation, the electric field 3200forms an angle θ with respect to an edge of the core 3105. The value ofangle θ is determined by tan⁻¹((W−a)/L), where W is the width 3125, a isthe width 3130, and L is the length 3120. When the angle θ is betweenabout 0° and 20° the current density may be optimized. This occurs when0<(W−a)/L<0.37.

FIG. 33 illustrates the current density in the core 3105 duringoperation. As shown, the current density is not concentrated at one sideof the core 3105 but, rather, is distributed at opposite sides proximateanode connector 3110 and cathode connector 3115. The current densityproximate the middle of the core 3105 is reduced compared with FIG. 30.Consequently, the central portion of the core 3105 is not subject tosignificant temperature elevations. Further, temperature variations arenot concentrated at a single side of the core 3105.

FIG. 34 is a table comparing the performance of a battery constructed inaccordance with FIG. 30 (designated battery A) versus a batteryconstructed in accordance with FIG. 31 (designated battery B). Thecolumns of FIG. 34 correspond to the following values:

-   -   Column 3405 corresponds to the number of discharge/re-charge        cycles for each battery;    -   Column 3410 corresponds to the battery capacity after the number        of cycles shown in column 3405;    -   Column 3415 corresponds to the ratio of the current battery        capacity to the original battery capacity after the number of        cycles shown in column 3405;    -   Column 3420 corresponds to the maximum temperature proximate the        anode connector that occurs during operation of the battery        after it has been subject to the number of cycles shown in        column 3405;    -   Column 3425 corresponds to the maximum temperature proximate the        cathode connector that occurs during operation of the battery        after it has been subject to the number of cycles shown in        column 3405; and    -   Column 3430 corresponds to the maximum temperature proximate the        center of the core that occurs during operation of the battery        after it has been subject to the number of cycles shown in        column 3405.

As shown, there are significant differences between the performanceparameters of battery A and battery B. The performance differencesbecome increasingly evident as the battery undergoes morecharge/recharge cycles. Consequently, the performance of battery B isbetter than battery A over time and battery B has a greater longevity.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible within the scope of theinvention. Accordingly, the invention is not to be restricted except inlight of the attached claims and their equivalents.

1. A battery system for storing electrical power and supplyingelectrical power to a vehicle comprising: multiple battery packs, eachbattery pack comprising a plurality of cells, wherein the cells in eachbattery pack are electrically connected with one another within therespective battery pack, and wherein the multiple battery packs areelectrically connected with one another to provide electrical power fromthe cells of the multiple battery packs to the vehicle, and wherein theelectrical connections between at least some of the cells include aseverable feature, whereby the electrical connection is severed locallyat the severable feature in response to an impact force that is inexcess of a predetermined magnitude or an overcurrent/overtemperaturecondition.
 2. The system of claim 1, wherein the cells are electricallyconnected to each other by mechanically connecting a positive terminalof one cell to a negative terminal on an adjacent cell, and wherein theseverable feature is a thinned portion of the positive and/or negativeterminal which will break when subject to the excessive impact force. 3.The system of claim 2, further comprising a ductile, conductive metaldeposited in the thinned portion, whereby the thinned portion does notadversely affect the conductivity of the positive and/or negativeterminal to a substantial degree, while the ductile, conductive metaldoes not prevent breaking of the thinned portion in response to theexcessive impact force.
 4. The system of claim 2, wherein the severablefeature comprises a mechanically weakened structure formed by an arcuateregion at a junction between the positive and negative terminals.
 5. Thesystem of claim 4, wherein the positive and negative terminals each havean arcuate region, and where the arcuate regions overlie one another atan interconnection region at which the positive and negative terminalsare connected with one another.
 6. The system of claim 1, wherein theseverable feature comprises at least some electrical terminals having amechanically weakened region at which the electrical connection betweenthe electrical terminals is severed in response to an impact force inexcess of a predetermined magnitude.
 7. The system of claim 6, whereinthe mechanically weakened region comprises a region of the electricalterminal that is thinned in comparison to other regions of the firstand/or second electrical terminals.
 8. The system of claim 7, furthercomprising a ductile, conductive metal deposited in the thinned regionof the electrical terminals, whereby the thinned region does notadversely affect the conductivity of electrical terminals to asubstantial degree, while the ductile, conductive metal does not preventthe electrical terminals from electrically severing from one another atthe thinned region in response to the excessive impact force.
 9. Thesystem of claim 1, wherein the severable feature comprises anovercurrent/overtemperature protection feature comprising a bondingmaterial used to facilitate electrical connection between at least someof the cells, the bonding material having a melting point thatcorresponds to an overcurrent/overtemperature condition between thecells, and wherein the bonding material is released from the electricalconnection having the overcurrent/overtemperature protection featurewhen the bonding material melts.
 10. The system of claim 9, wherein theovercurrent/overtemperature protection feature comprises: a firstelectrical terminal electrically connected to a core of a first cell andhaving a first connection face; a second electrical terminalelectrically connected to a core of a second cell and having a secondconnection face; wherein the bonding material facilitates electricalconnection between the first and second connection faces of the firstand second electrical terminals at an electrical junction.
 11. Thesystem of claim 10, further comprising an insulating member disposed atthe electrical junction between the first and second connection faces,the insulating member having a thermal coefficient of expansion at themelting temperature of the bonding material sufficient to drive thefirst and second connection faces apart to facilitate removal of thebonding material from between the first and second connection faces. 12.The system of claim 11, wherein the insulating member expands asufficient amount at the melting temperature of the bonding material toovercome surface tension of the melted bonding material at the first andsecond connection faces.
 13. The system of claim 11, further comprisinga mass disposed at the junction between first and second connectionfaces that is removed from the junction under the influence of gravitywhen the bonding material melts.
 14. The system of claim 13, wherein theelectrical connection between the first and second connection facescomprises: a first layer of the bonding material between the firstconnection face and a first side of the mass; a second layer of thebonding material between the second connection face and a second side ofthe mass; and wherein the first and second layers of the bondingmaterial are completely physically separated from one another by themass.
 15. The system of claim 1, wherein the severable feature comprisesan overcurrent/overtemperature protection feature that comprises layersof a structure at the terminals of at least some of the cells which havedifferent thermal coefficients of expansion that cause the layers tosever the electrical connection at terminals in response to anovercurrent/overtemperature condition.
 16. The system of claim 15,wherein the overcurrent/overtemperature protection feature comprises: afirst electrical terminal electrically connected to a core of a firstcell and having a first connection face, the first electrical terminalfurther having a first opposed face opposite the first connection face;a second electrical terminal electrically connected to a core of asecond cell and having a second connection face, the second electricalterminal further having a second opposed face opposite the secondconnection face; wherein the multilayer clamp is disposed to insert asevering force on the first and second opposed faces.
 17. The system ofclaim 16, wherein the multilayer clamp comprises: a first layer adjacentthe first and second opposed faces; a second layer exterior to the firstlayer; wherein the first layer has a higher thermal coefficient ofexpansion than the second layer, whereby the expansion of the firstlayer is constrained by the second layer so that the first layer isdriven toward the first and second opposed faces to sever the electricalconnection between the first and second terminals in response to theovercurrent/overtemperature condition.
 18. The system of claim 1,wherein the severable feature comprises an overcurrent/overtemperatureprotection feature located at the electrical terminals of at least someof the cells in which a chemical is released onto the electricalconnection in response to an overcurrent/overtemperature condition tochemically attack and sever the electrical connection.
 19. The system ofclaim 18, wherein the overcurrent/overtemperature protection featurecomprises: a caustic material that chemically attacks a bonding materialat the electrical connection; and a container for the caustic material,wherein the container is formed from a material that melts at atemperature corresponding to the overcurrent/overtemperature condition.20. The system of claim 1, wherein the electrical connections between atleast some of the cells include an overcurrent/overtemperatureprotection feature in which a liquid conductor is removed from theelectrical connection in response to an overcurrent/overtemperature tothereby electrically disconnect the connection.
 21. The system of claim20, wherein the overcurrent/overtemperature protection featurecomprises: a container spanning a gap between terminals of theelectrical connection, the container being formed from a material havinga melting point corresponding to the overcurrent/overtemperaturecondition; and a liquid conductor disposed in the container andelectrically connecting terminals of the electrical connection, whereinthe container melts in response to the overcurrent/overtemperaturecondition to release the liquid conductor from the gap therebyelectrically disconnecting the terminals of the electrical connection.22. The system of claim 21, wherein the overcurrent/overtemperatureprotection feature comprises: a conduction chamber holding the liquidconductor to span a gap between terminals of the electrical connectionunder normal operating conditions; a collection chamber disposed at anelevation below the conduction chamber; and a sealing member disposedbetween the conduction chamber and collection chamber, wherein thesealing member is adapted to melt at a temperature corresponding to theovercurrent/overtemperature condition, whereby the liquid conductordrains from the conduction chamber to the collection chamber toelectrically disconnect the connection when the sealing member melts.23. A battery system comprising: a first battery cell having a firstelectrical terminal, and a second battery cell having a secondelectrical terminal, wherein the first and second battery cells aresecured with one another as a battery pack so that the first and secondelectrical terminals are separated from one another by a gap; anovercurrent/overtemperature protection structure proximate theconnection region comprising a conduction chamber including a liquidconductor, wherein the conduction chamber is positioned so that theliquid conductor spans the gap to facilitate electrical current flowbetween the first and second electrical terminals under normal operatingconditions, a collection chamber disposed at an elevation below theconduction chamber, a wall disposed between the conduction chamber andthe collection chamber, wherein the wall includes an opening between theconduction chamber and collection chamber, a sealing member formed froma material having a melting point that is selected to correspond to anovercurrent/overtemperature condition at the first and second electricalterminals, where the sealing member prevents leakage of the liquidconductor from the conduction chamber to the collection chamber duringnormal operating conditions, and where the sealing member melts duringan overcurrent/overtemperature condition at the first and secondelectrical terminals to allow the liquid conductor to drain from theconduction chamber and into the collection chamber thereby severing theelectrical connection between the first and second electrical terminals.24. A battery system comprising: a first battery cell having a firstelectrical terminal, and a second battery cell having a secondelectrical terminal, wherein the first and second electrical terminalsare secured with one another at a connection region; anovercurrent/overtemperature protection structure proximate theconnection region comprising a container formed from a material having amelting point that is selected to correspond to anovercurrent/overtemperature condition at the first and second electricalterminals, a connection degrading agent in the container, wherein theconnection degrading agent is released from the container proximate theconnection region as the container melts to facilitate chemicaldestruction of the interconnection between the first and secondelectrical when an overcurrent/overtemperature occurs at the first andsecond electrical terminals.
 25. A battery system for storing electricalpower and supplying electrical power to drive a vehicle comprising: afirst battery cell having a first electrical terminal, and a secondbattery cell having a second electrical terminal, wherein the first andsecond battery cells are secured immediately adjacent one another in abattery pack so that the first and second electrical terminals areseparated from one another by a gap; and a rigid conductive bridge pieceadapted for bonding with the first and second electrical terminalsthereby establishing an electrical and mechanical connection between thefirst and second electrical terminals over the gap.
 26. The batterysystem of claim 25, wherein the first electrical terminal has a firstconnection face and the second electrical terminal has a secondconnection face that is substantially parallel to the first connectionface, and where the rigid conductive bridge piece is connected to thefirst and second connection faces.
 27. The battery system of claim 26,wherein the first and second connection faces are oriented to face oneanother.
 28. The battery system of claim 27, wherein the rigidconductive bridge piece comprises: a first layer formed from aconductive material and connected to the first and second connectionfaces; and a second layer that is disposed over and bonded with thefirst layer, wherein the second layer is formed from a memory alloywhich pulls the first layer from contact with the first and/or secondconnection faces when a temperature at the first and second terminalsreaches a level corresponding to an overcurrent/overtemperaturecondition.
 29. The battery system of claim 26, wherein the first andsecond connection faces are oriented to face away from one another. 30.The battery system of claim 29, wherein the rigid conductive bridgepiece comprises: a first metal layer connected to the first and secondconnection faces; and a second metal layer that is disposed over andbonded with the first metal layer, wherein the first and second metallayers have different thermal expansion coefficients so that the rigidconductive bridge piece separates from the first and/or secondconnection face at a temperature corresponding to anovercurrent/overtemperature condition.